Add assistant actions in the suggestion bar

[julien-nc]

There could be assistant-related actions suggested as a button next to the ones that appear when the document is empty.

For example:

• Insert audio transcription
• Insert generated text
• Insert generated image

cc @blizzz

[juliusknorr]

I'd be rather careful to add even more, the ui already feels rather cluttered, but leaving it to the designers :)

[marcoambrosini]

I think it's fine to add them since this buttons go away when the user starts typing, and also given the fact that we'll probably remove the ever present assistant button. There could be a second row of buttons with AI actions there.

A couple of somewhat related things that would improve UX:

• [ ] #7795
• [ ] #7796