[MM-40712] config: Bugfix on path resolution; fail if given config does not exist (#19360)

* config: bugfix on path resolution; fail if given config does not exist

* reflect review comments

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

app/options.go

@@ -45,7 +45,7 @@ func StoreOverride(override interface{}) Option {
 // config loaded from the dsn on top of the normal defaults
 func Config(dsn string, readOnly bool, configDefaults *model.Config) Option {
 	return func(s *Server) error {
-		configStore, err := config.NewStoreFromDSN(dsn, readOnly, configDefaults)
+		configStore, err := config.NewStoreFromDSN(dsn, readOnly, configDefaults, true)
 		if err != nil {
 			return errors.Wrap(err, "failed to apply Config option")
 		}

app/server.go

@@ -210,7 +210,7 @@ func NewServer(options ...Option) (*Server, error) {
 	//
 	// Step 1: Config.
 	if s.configStore == nil {
-		innerStore, err := config.NewFileStore("config.json")
+		innerStore, err := config.NewFileStore("config.json", true)
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to load config")
 		}

app/server_test.go

@@ -168,7 +168,7 @@ func TestStartServerNoS3Bucket(t *testing.T) {
 	s3Endpoint := fmt.Sprintf("%s:%s", s3Host, s3Port)
 
 	s, err := NewServer(func(server *Server) error {
-		configStore, _ := config.NewFileStore("config.json")
+		configStore, _ := config.NewFileStore("config.json", true)
 		store, _ := config.NewStoreFromBacking(configStore, nil, false)
 		server.configStore = store
 		server.UpdateConfig(func(cfg *model.Config) {