MM-14439: experimental restrict system admin (#10414)

* api4: break out license and config from system

* app: move some config functions from admin.go to config.go

* add ExperimentalSettings.RestrictSystemAdmin

* forbid various actions to restricted system admin

* update default.json

* fix function names in errors

api4/cluster.go

@@ -19,6 +19,11 @@ func getClusterStatus(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if *c.App.Config().ExperimentalSettings.RestrictSystemAdmin {
+		c.Err = model.NewAppError("getClusterStatus", "api.restricted_system_admin", nil, "", http.StatusForbidden)
+		return
+	}
+
 	infos := c.App.GetClusterStatus()
 	w.Write([]byte(model.ClusterInfosToJson(infos)))
 }