Improve UX when updating

[lidel]

Right now user can manually force update via About → Check for Updates
but they don't get any feedback until its done or fails. Downloading updates may take time on slower connection, producing experience where nothing happens for a long long time.

We could:

• at least do what we do for GC, and set status in menu to Running (Fetching Update) (feat(ux): improve gc #1420 (comment)).
• (optional) additionally, we could pass progress to webui when opened (inspiration: Auto update application unipept/unipept-desktop#35 (comment))

[jessicaschilling]

Both these options are clear and consistent with how we are already doing things. I’d suggest both.

[jessicaschilling]

Menu text changes:

• Gray out "Check for Updates..." and replace text with "Checking for Updates"
• Replace menu status with yellow dot (same as GC) and "Running (Checking for Updates)"

Snackbar feedback text:

• If failed, failure-specific message (what types of failure other than "could not download" do we have?) with link to troubleshoot: at minimum, dist page
• Is there a need for an additional "taking a long time" message or does this just turn into failure on timeout?