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 75.74%. Comparing base (5c9d144) to head (b9eb027).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1375   +/-   ##
=======================================
  Coverage   75.74%   75.74%           
=======================================
  Files          17       17           
  Lines        4391     4391           
  Branches      667      667           
=======================================
  Hits         3326     3326           
  Misses        833      833           
  Partials      232      232           

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