[MM-38082] Add local-mode handler for config reload endpoint (#18252)

* Add local-mode handler for config reload endpoint

* Remove redundant method

api4/config.go

@@ -86,12 +86,15 @@ func configReload(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if *c.App.Config().ExperimentalSettings.RestrictSystemAdmin {
+	if !c.AppContext.Session().IsUnrestricted() && *c.App.Config().ExperimentalSettings.RestrictSystemAdmin {
 		c.Err = model.NewAppError("configReload", "api.restricted_system_admin", nil, "", http.StatusBadRequest)
 		return
 	}
 
-	c.App.ReloadConfig()
+	if err := c.App.ReloadConfig(); err != nil {
+		c.Err = model.NewAppError("configReload", "api.config.reload_config.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return
+	}
 
 	auditRec.Success()