DPE-9158 Speedup action list-backups (from minutes to seconds)

[taurus-forever]

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 76.07%. Comparing base (37da95b) to head (bd1cafe).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1375   +/-   ##
=======================================
  Coverage   76.07%   76.07%           
=======================================
  Files          16       16           
  Lines        4314     4314           
  Branches      665      665           
=======================================
  Hits         3282     3282           
  Misses        801      801           
  Partials      231      231           

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