ABC-176 Prevent changing PluginSettings.EnableUploads through the API (#8249)

* Prevent changing PluginSettings.EnableUploads through the API

* Contain api4 test case in it's own test

api4/system.go

@@ -121,6 +121,9 @@ func updateConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Do not allow plugin uploads to be toggled through the API
+	cfg.PluginSettings.EnableUploads = c.App.GetConfig().PluginSettings.EnableUploads
+
 	err := c.App.SaveConfig(cfg, true)
 	if err != nil {
 		c.Err = err