Prevent synced CPA values to be updated from the API (#30687)

* Prevents the API from updating synced CPA values

The patch functions for CPA values now accept a parameter that checks
if they should allow for synced values to be updated, and prevent
those updates if necessary

* Fix linter

* Fix parameter after merge

---------

Co-authored-by: Miguel de la Cruz <miguel@ctrlz.es>
Co-authored-by: Scott Bishel <scott.bishel@mattermost.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/i18n/en.json

@@ -5078,6 +5078,10 @@
     "id": "app.custom_profile_attributes.property_field_delete.app_error",
     "translation": "Unable to delete Custom Profile Attribute field"
   },
+  {
+    "id": "app.custom_profile_attributes.property_field_is_synced.app_error",
+    "translation": "Cannot update value for a synced Custom Profile Attribute field"
+  },
   {
     "id": "app.custom_profile_attributes.property_field_not_found.app_error",
     "translation": "Custom Profile Attribute field not found"