Make configs and translations publishable

[aerni]

I had to open a new PR because I had to change the target branch. This is the same PR as #2135.

Summary

An addon's config and translations now automatically merge and load.

You can also publish the files:

// Config
vendor:publish --tag="addon-slug-config"

// Translations
vendor:publish --tag="addon-slug-translations"

If you don't want to merge the config and load the translations you can opt-out of it by setting the following properties in the addon's Service Provider:

protected $config = false;
protected $translations = false;