[MM-30436] Add support for configuration custom defaults (#16265)

* [MM-30436] Add support for configuration custom defaults

* Addressing review comments

* Addressing PR comments

* Soft fail if the configuration defaults cannot be read

* Directly print error in log message

* Fix linter

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/apitestlib.go

@@ -92,7 +92,7 @@ func setupTestHelper(dbStore store.Store, searchEngine *searchengine.Broker, ent
 	}
 	memoryStore.Set(memoryConfig)
 
-	configStore, err := config.NewStoreFromBacking(memoryStore)
+	configStore, err := config.NewStoreFromBacking(memoryStore, nil)
 	if err != nil {
 		panic(err)
 	}