Fix review feedback: override warnings and search docs

Add explicit deprecation warnings in override and makeWithOverrides when
config.schema is used, since the merged result now passes through
configSchema. Update search declarative-integration docs to use
SearchResultListItemBlueprint instead of the removed extension creator.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

packages/frontend-plugin-api/src/wiring/createExtension.ts

@@ -689,6 +689,10 @@ export function createExtension(
         );
       }
 
+      if (overrideOptions.config?.schema) {
+        warnConfigSchemaPropDeprecation(describeParentCallSite());
+      }
+
       // TODO(Rugvip): Making this a type check would be optimal, but it seems
       //               like it's tricky to add that and still have the type
       //               inference work correctly for the factory output.

packages/frontend-plugin-api/src/wiring/createExtensionBlueprint.ts

@@ -38,6 +38,8 @@ import {
 import { ExtensionDataContainer } from './types';
 import { PageBlueprint } from '../blueprints/PageBlueprint';
 import { FilterPredicate } from '@backstage/filter-predicates';
+import { warnConfigSchemaPropDeprecation } from '../schema/createPortableSchema';
+import { describeParentCallSite } from '../routing/describeParentCallSite';
 
 /**
  * A function used to define a parameter mapping function in order to facilitate
@@ -729,6 +731,9 @@ export function createExtensionBlueprint(options: any): any {
       }) as OverridableExtensionDefinition;
     },
     makeWithOverrides(args: any) {
+      if (args.config?.schema) {
+        warnConfigSchemaPropDeprecation(describeParentCallSite());
+      }
       return createExtension({
         kind: options.kind,
         name: args.name,