[Data views as code] Add field filters to saved schema (elastic#270538)

## Summary

Related to elastic#262225

Field filters can be used to exclude fields when fetching a document. In
the original as code saved data view object it wasn't added, but it
should.


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [x] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

Author: AlexGPlay

src/platform/packages/shared/as-code/data-views-schema/src/data_views/schema_saved_data_view.test.ts

@@ -80,6 +80,41 @@ describe('savedDataViewSpecSchema', () => {
     );
   });
 
+  it('accepts field_filters as an array of strings', () => {
+    const input = {
+      index_pattern: 'logs-*',
+      field_filters: ['field_a', 'field_b'],
+    };
+
+    expect(savedDataViewSpecSchema.validate(input)).toEqual(input);
+  });
+
+  it('accepts an empty field_filters array', () => {
+    const input = {
+      index_pattern: 'logs-*',
+      field_filters: [],
+    };
+
+    expect(savedDataViewSpecSchema.validate(input)).toEqual(input);
+  });
+
+  it('accepts spec without field_filters', () => {
+    const input = {
+      index_pattern: 'logs-*',
+    };
+
+    expect(savedDataViewSpecSchema.validate(input)).toEqual(input);
+  });
+
+  it('rejects field_filters with non-string values', () => {
+    const input = {
+      index_pattern: 'logs-*',
+      field_filters: [123],
+    };
+
+    expect(() => savedDataViewSpecSchema.validate(input)).toThrow();
+  });
+
   it('rejects an empty field_settings key', () => {
     const input = {
       index_pattern: 'logs-*',

src/platform/packages/shared/as-code/data-views-schema/src/data_views/schema_saved_data_view.ts

@@ -62,6 +62,16 @@ export const savedDataViewSpecSchema = schema.object(
         },
       })
     ),
+    field_filters: schema.maybe(
+      schema.arrayOf(schema.string({ minLength: 1, maxLength: 1000 }), {
+        maxSize: 10_000,
+        meta: {
+          title: 'Field filters',
+          description:
+            "Field filters can be used to exclude one or more fields when fetching a document. They may contain wildcards, such as `user*` which filters fields starting with 'user'.",
+        },
+      })
+    ),
     index_pattern: indexPatternSchema,
     time_field: timeFieldSchema,
     field_settings: schema.maybe(

src/platform/packages/shared/as-code/data-views-transforms/src/from_stored_data_view.test.ts

@@ -161,4 +161,34 @@ describe('fromStoredDataViewToAsCodeSavedSchema', () => {
       },
     });
   });
+
+  it('maps sourceFilters to field_filters', () => {
+    expect(
+      fromStoredDataViewToAsCodeSavedSchema({
+        title: 'logs-*',
+        sourceFilters: [{ value: 'field_a' }, { value: 'field_b' }],
+      })
+    ).toEqual(
+      expect.objectContaining({
+        field_filters: ['field_a', 'field_b'],
+      })
+    );
+  });
+
+  it('omits field_filters when sourceFilters is empty', () => {
+    const result = fromStoredDataViewToAsCodeSavedSchema({
+      title: 'logs-*',
+      sourceFilters: [],
+    });
+
+    expect(result).not.toHaveProperty('field_filters');
+  });
+
+  it('omits field_filters when sourceFilters is absent', () => {
+    const result = fromStoredDataViewToAsCodeSavedSchema({
+      title: 'logs-*',
+    });
+
+    expect(result).not.toHaveProperty('field_filters');
+  });
 });

src/platform/packages/shared/as-code/data-views-transforms/src/from_stored_data_view.ts

@@ -61,5 +61,9 @@ export function fromStoredDataViewToAsCodeSavedSchema(index: DataViewSpec): AsCo
     time_field: index.timeFieldName,
     allow_hidden_indices: index.allowHidden,
     field_settings: fieldSettings,
+    ...(index.sourceFilters &&
+      index.sourceFilters.length > 0 && {
+        field_filters: index.sourceFilters.map((sourceFilter) => sourceFilter.value),
+      }),
   };
 }

src/platform/packages/shared/as-code/data-views-transforms/src/to_stored_data_view.test.ts

@@ -15,6 +15,7 @@ import {
   type AsCodeSavedDataView,
 } from '@kbn/as-code-data-views-schema';
 import { toStoredDataView } from './to_stored_data_view';
+import type { DataViewSpec } from '@kbn/data-views-plugin/common';
 
 describe('toStoredDataView', () => {
   it('converts data_view_reference data_source to string id', () => {
@@ -154,5 +155,35 @@ describe('toStoredDataView', () => {
         },
       });
     });
+
+    it('maps field_filters to sourceFilters', () => {
+      const dataView: AsCodeSavedDataView = {
+        id: 'dv-1',
+        index_pattern: 'logs-*',
+        field_filters: ['field_a', 'field_b'],
+      };
+
+      const result = toStoredDataView(dataView);
+      expect(result).toEqual(
+        expect.objectContaining({
+          sourceFilters: [{ value: 'field_a' }, { value: 'field_b' }],
+        })
+      );
+    });
+
+    it('omits sourceFilters when field_filters is undefined', () => {
+      const dataView: AsCodeSavedDataView = {
+        id: 'dv-2',
+        index_pattern: 'logs-*',
+      };
+
+      const result = toStoredDataView(dataView);
+      expect(result).toEqual(
+        expect.objectContaining({
+          title: 'logs-*',
+        })
+      );
+      expect((result as DataViewSpec).sourceFilters).toBeUndefined();
+    });
   });
 });

src/platform/packages/shared/as-code/data-views-transforms/src/to_stored_data_view.ts

@@ -49,7 +49,12 @@ export function toStoredDataView(
 function isSavedDataView(
   dataView: AsCodeDataView | AsCodeSavedDataView
 ): dataView is AsCodeSavedDataView {
-  return 'id' in dataView || 'name' in dataView || 'allow_hidden_indices' in dataView;
+  return (
+    'id' in dataView ||
+    'name' in dataView ||
+    'allow_hidden_indices' in dataView ||
+    'field_filters' in dataView
+  );
 }
 
 function getSavedDataViewFields(dataView: AsCodeSavedDataView): Partial<DataViewSpec> {
@@ -58,5 +63,6 @@ function getSavedDataViewFields(dataView: AsCodeSavedDataView): Partial<DataView
     id: dataView.id,
     name: dataView.name,
     allowHidden: dataView.allow_hidden_indices,
+    sourceFilters: dataView.field_filters?.map((filter) => ({ value: filter })),
   };
 }