Tor Connection appearance: implement February sprint outcome

This is moved from #17215 (closed), so refer to that for more information.

• generally improve aesthetics: margins, padding, etc. (done in !428 (merged))

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• make the progress bar go smoothly, even when there is no "real" progress (done in !426 (merged))

• redesign the error step (mostly done in !428 (merged))

  

  vs.

  

• in "hide mode", explain bridge requirements upfront

I propose to add more info text below "Type in a bridge" when hiding Tor:

Currently in Tails, only obfs4 bridges hide that you are using Tor.

obfs4 bridges start with the word 'obfs4'.

To request obfs4 bridges, you can send an empty email to
bridges@torproject.org from a Gmail or Riseup email address.

I only got obfs4 when I sent an email.