Enhance update_status to monitor health checks and collect diagnostic logs

[marceloneppel]

Issue

Solution

Previously, the update_status hook only checked if the PostgreSQL pebble service was active. This could miss situations where the service appeared running but the health check was failing. This change enhances the restart logic to also monitor Pebble health check status and collect diagnostic information when issues are detected.

Changes:

• Monitor Pebble health check status in addition to service status
• Trigger restart when health check is DOWN even if service is ACTIVE
• Add _get_postgresql_startup_logs() to collect diagnostic information from Pebble logs and PostgreSQL logs before and after restart attempts
• Add comprehensive unit tests for health check monitoring and error handling

This improves observability and helps diagnose PostgreSQL restart issues by capturing relevant logs at the time of failure.

Checklist

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

[codecov]

Codecov Report

❌ Patch coverage is 67.85714% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.82%. Comparing base (2109c90) to head (fde7ee5).

Files with missing lines	Patch %	Lines
src/charm.py	67.85%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1192      +/-   ##
==========================================
- Coverage   72.85%   72.82%   -0.04%     
==========================================
  Files          15       15              
  Lines        4012     4040      +28     
  Branches      597      599       +2     
==========================================
+ Hits         2923     2942      +19     
- Misses        863      871       +8     
- Partials      226      227       +1     

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[taurus-forever]

Nice PR and interesting findings right out of the box: ERROR cannot start service while killing

[marceloneppel]

Nice PR and interesting findings right out of the box: ERROR cannot start service while killing

Hopefuly, this PR is the solution for the issue that we saw when upgrading PG to 14.20. I believe the new PG is working a little bit different and Pebble from Juju 2.9 is not correctly detecting that Patroni is stopped (it seems that Pebble is seeing PG still running and considering the Patroni service - PG process parent - still active because of that).

Regarding the finding you commented, I believe that error may be a side effect of the fix added by this PR. It will need more investigation.