fix: pass streamdeck cli validate errors and warnings

[deverman]

When trying to validate the plug-in I am creating with the StreamDeck CLI tool I found that the manifest.json was missing the UUID for the plugin which is required.

I modified the PluginManifest.swift and StreamDeckPlugin.swift to support outputting the UUID to the manifest.json file.

To test this I built and validated the counter plugin. In doing so there were some additional validation errors.

• Some could be fixed by documenting exact commands and parameters to build the plugin
• Others required adding dummy icon resources
• And finally some values needed to be added CounterPlugin.swift including the uuid which I designated as "com.example.counter". Actions had to be updated with this full UUID as well.

To make sure there is a shared understanding how to build the plugins I created README.md in the counter example directory.

Let me know if you need any clarifications or changes to this PR.

[emorydunn]

Thanks for putting this together. Not sure when the UUID was added to the manifest, I don't see it in the SDK changelog. I'll take a look at the changes over the weekend.