feat(problem+json): Add support for application/problem+json

Although rfc9457 is still in proposed status, support was already
added in Java Spring environment and thus it is live in the wild.

To support this while also not yet adding a huge new mechanism just
warn that MUST declarations are currently not enforced by ogen.

To test this sprinkle problem+json into various test files.

Author: AndreasBergmeier6176

_testdata/examples/api.github.com.json

@@ -166,7 +166,7 @@
           "200": {
             "description": "Response",
             "content": {
-              "application/json": {
+              "application/problem+json": {
                 "schema": {
                   "type": "object",
                   "properties": {
@@ -96299,4 +96299,4 @@
       }
     }
   }
-}
+}

_testdata/examples/k8s.json

@@ -1863,7 +1863,7 @@
         ],
         "requestBody": {
           "content": {
-            "application/json-patch+json": {
+            "application/problem+json": {
               "schema": {
                 "$ref": "#/components/schemas/io.k8s.apimachinery.pkg.apis.meta.v1.Patch"
               }

_testdata/examples/problemjson.yml

@@ -0,0 +1,60 @@
+openapi: 3.0.1
+info:
+  version: 1.0.0
+  title: API with Problems
+paths:
+  /v1/test:
+    get:
+      operationId: getTest
+      responses:
+        "200":
+          x-summary: OK
+          description: Process me.
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  message:
+                    type: string
+                    example: "Hello, World!"
+        "400":
+          x-summary: Bad Request
+          description: |
+            Something was wrong
+          content:
+            application/problem+json:
+              schema:
+                $ref: '#/components/schemas/ProblemJsonErrorResponse'
+
+components:
+  schemas:
+    ProblemJsonErrorResponse:
+      type: object
+      description: >-
+        An errors that occurred.
+      required:
+        - type
+        - title
+        - status
+      properties:
+        type:
+          type: string
+          description: >-
+            Identifies the type of the problem. If the problem type has no additional semantics beyond the HTTP status code, the URI `about:blank` is used.
+          example: "about:blank"
+        title:
+          type: string
+          description: >-
+            Roughly describes the problem. This is a static description, not a detailed one. If `type` is `about:blank`, the reason phrase of the status should be used as title.
+          example: Not Found
+        status:
+          type: integer
+          format: int32
+          description: HTTP status code.
+          example: 404
+        detail:
+          type: string
+          description: >-
+            Further details about the error.
+          example: The email address could not be found.