Move parameter & return annotation type details

[lucyleeow]

📚 New content request

Currently we detail parameter and return annotation types we support and what each do in our page on magicgui widgets: https://napari.org/dev/howtos/extending/magicgui.html#parameter-annotations

Now that we also have app-model providers and processors, these now generalise to all actions, not just magicgui widgets. We should move the annotation type details to their own page or a new page detailing how users should use actions.

AFAICT there is no documentation about users writing app-model actions, I think this is related to this not being implemented yet: napari/napari#7312

Related to this discussion on zulip.

CC @DragaDoncila @jni