DPE-9158 Speedup action list-backups by list archive only

[taurus-forever]

Backport #1375 to PG16.

Issue

At the moment charm action list-backups executes minutes on S3 buckets with hundreds backups,
while some common backups have thousand of backups causing action timeout.

The often config is hold backups for 30 days with nightly full backup and incremental backup each 15 minutes.

Solution

List S3 content recursively for archive part only. It will be enough to generate Timelines list.
This will skip the biggest neighbor folder backups, which used to eat most of the time in _list_timelines().

Checklist

• I have added or updated any relevant documentation.
• I have cleaned any remaining cloud resources from my accounts.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.53%. Comparing base (536bfa9) to head (caf6e46).

Additional details and impacted files

@@           Coverage Diff            @@
##           16/edge    #1376   +/-   ##
========================================
  Coverage    70.53%   70.53%           
========================================
  Files           16       16           
  Lines         4297     4297           
  Branches       691      691           
========================================
  Hits          3031     3031           
  Misses        1055     1055           
  Partials       211      211           

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