Refactor API structure and update schema references

Moved API files from `sub_api` to `schemas` for better organization. Updated schema references to use `ApiError` instead of `Error`. Adjusted build configuration to include new schema folder in the API generation process.

open_api/src/main/resources/schemas/generic/errors.yml

@@ -0,0 +1,7 @@
+components:
+  schemas:
+    ApiError:
+      type: object
+      properties:
+        reason:
+          type: string