[draft] Use s3-integrator from 2/edge channel with s3 charm lib v1

[theoctober19th]

This PR aims to upgrade the postgres charm in 16/edge to use the new s3 charm lib, and also bump to use charm from 2/edge in the CI.

The PR also releases the charm on a test branch on channel 16/edge/pr so that we can then test this charm in the s3-integrator integration tests.

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 68.56%. Comparing base (3d1ef44) to head (daf0a0b).
⚠️ Report is 11 commits behind head on 16/edge.

❌ Your project check has failed because the head coverage (68.56%) is below the target coverage (70.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff            @@
##           16/edge    #1280   +/-   ##
========================================
  Coverage    68.56%   68.56%           
========================================
  Files           16       16           
  Lines         3868     3868           
  Branches       590      590           
========================================
  Hits          2652     2652           
  Misses        1008     1008           
  Partials       208      208           

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