[DPE-6662] Fix pgbackrest logs names on logs rotation

[taurus-forever]

Issue

Reported as https://warthogs.atlassian.net/browse/DPE-6662

The pgBackRest activity (backup creation, stanza initialization, etc) could take minutes,
as a result every minute logs rotation could move the current log A.log to A.log_$date.log and
will be moved the next minute further as logrorate rule operates all *.log files in the folder:

/var/snap/charmed-postgresql/common/var/log/pgbackrest/*.log { ...

It results in:

-rw------- 1 postgres postgres     0 Feb 18 09:25 all-server.log
-rw------- 1 postgres postgres     0 Feb 18 09:19 all-server.log-20250218_09:18.log
-rw------- 1 postgres postgres     0 Feb 18 09:20 all-server.log-20250218_09:18.log-20250218_09:19.log
-rw------- 1 postgres postgres     0 Feb 18 09:21 all-server.log-20250218_09:18.log-20250218_09:19.log-20250218_09:20.log
-rw------- 1 postgres postgres     0 Feb 18 09:22 all-server.log-20250218_09:18.log-20250218_09:19.log-20250218_09:20.log-20250218_09:21.log
-rw------- 1 postgres postgres     0 Feb 18 09:23 all-server.log-20250218_09:18.log-20250218_09:19.log-20250218_09:20.log-20250218_09:21.log-20250218_09:22.log
-rw------- 1 postgres postgres  1793 Feb 18 09:24 all-server.log-20250218_09:18.log-20250218_09:19.log-20250218_09:20.log-20250218_09:21.log-20250218_09:22.log-20250218_09:23.log

The same time pgBackRest files names are wide and complex and depends on Juju application name (and more),
therefor there are no K.I.S.S way to reconfigure logrotare rules avoiding *.log.

Solution

• move the log file to the new name without .log suffix
• use datetime format matching MySQL charms

Example:

-rw------- 1 postgres postgres    12 Feb 18 09:28 all-server.log
-rw------- 1 postgres postgres   322 Feb 18 09:29 all-server.log-20250218_0918
-rw------- 1 postgres postgres  7344 Feb 18 09:30 all-server.log-20250218_0918

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 70.22%. Comparing base (2bb989c) to head (235ab76).
Report is 6 commits behind head on 16/edge.

Additional details and impacted files

@@           Coverage Diff            @@
##           16/edge     #939   +/-   ##
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  Coverage    70.22%   70.22%           
========================================
  Files           16       16           
  Lines         3725     3725           
  Branches       542      542           
========================================
  Hits          2616     2616           
  Misses         974      974           
  Partials       135      135           

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