[DPE-8473] Handle invalid database name (databases)

[marceloneppel]

Issue

With the new predefined roles implemented for PG 16, if a client app requests a database called databases while the PG charm tries to set up the roles for it, a failure will happen because one of the roles will conflict with the already existing charmed_databases_owner role (responsible for owning all the databases).

Solution

This PR is a follow-up from canonical/postgresql-single-kernel-library#18.

Port of canonical/postgresql-k8s-operator#1108.

The single kernel lib new version, which has the list of invalid databases, was already updated in a previous renovate PR. What this PR updates is the check that unblocks the charm on src/relations/postgresql_provider.py.

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 64.53%. Comparing base (45b23a2) to head (3658eaa).
⚠️ Report is 3 commits behind head on 16/edge.

❌ Your project status has failed because the head coverage (64.53%) 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    #1190   +/-   ##
========================================
  Coverage    64.53%   64.53%           
========================================
  Files           17       17           
  Lines         4339     4339           
  Branches       671      671           
========================================
  Hits          2800     2800           
  Misses        1357     1357           
  Partials       182      182           

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