Bug#1025762: gnome-session: Install and enable appindicator and desktop icons NG extensions

[Jeremy Bicha]

Here are merge proposals:

https://salsa.debian.org/gnome-team/gnome-shell/-/merge_requests/67
https://salsa.debian.org/gnome-team/gnome-session/-/merge_requests/11

And there's more explanation at https://bugs.debian.org/1025762

I'd like to land this soon so that it's included in Debian 12 and I'd
appreciate review first.

Thank you,
Jeremy Bicha