revert strict enforcement of "required" and "min" for relationships. See changelog for rationale. I made this mess, I am reverting it heh (#5039)

Author: boutell

CHANGELOG.md

@@ -15,6 +15,10 @@
 * The `?render-areas=1` API feature now correctly disregards areas in separate documents loaded via relationship fields. Formerly their presence resulted in an error, not a rendering.
 * Make conditional fields work in Image Editor.
 
+### Changes
+
+* Rolled back a change in 4.16.0 that strictly enforced `required` and `min` for relationship fields. Because the related document can be archived or deleted at any time, it is misleading to offer such enforcement. Also, it greatly complicates adding these constraints to existing schemas, resulting in surprising and unwanted behaviors. Therefore it is better for these constraints to be soft constraints on the front end. `max` is still a hard constraint.
+
 ## 4.20.0 (2025-08-06)
 
 ### Adds

modules/@apostrophecms/schema/lib/addFieldTypes.js

@@ -1183,12 +1183,9 @@ module.exports = (self) => {
         }
         destination[field.name] = actualDocs;
       }
-      if (field.required && (destination[field.name].length === 0)) {
-        throw self.apos.error('required');
-      }
-      if (field.min && field.min > destination[field.name].length) {
-        throw self.apos.error('min', `Minimum ${field.withType} required not reached.`);
-      }
+      // "min" and "required" are not enforced server-side for relationships because it is always possible
+      // for the related document to be removed independently at some point. This leads to too many
+      // edge cases and knock-on effects if enforced
       if (field.max && field.max < destination[field.name].length) {
         throw self.apos.error('max', `Maximum ${field.withType} required reached.`);
       }