Intro to plugin development: mention that Grafana has to be in development mode

[Omar Elbaghdadi]

I'm getting started on writing a plugin for the first time. After following the "Create a new plugin" section of https://grafana.com/tutorials/build-a-panel-plugin/#0, the created plugin wasn't being registered.

After looking through the logs, I saw this line:

logger=plugin.loader t=2022-05-13T12:15:18.93+0200 lvl=warn msg="Skipping loading plugin due to problem with signature" pluginID=my-plugin status=unsigned

From other documentation, I noticed that unsigned plugins are only allowed in development mode. After changing app_mode to development, the plugin can be loaded.

In my opinion, the steps in the documentation should make it clear that the app_mode should be changed to development in the config. It should also be made clear that after you have run yarn dev, your plugin is by default unsigned, and that Grafana won't load it unless the config is changed.

[Marcus Efraimsson]

The backend tutorial has a troubleshoot section mentioning this, but needs an update as well since it says backend plugins requires to be signed - nowadays all plugins required to be signed: https://grafana.com/tutorials/build-a-data-source-backend-plugin/#create-a-new-plugin