[DPE-7499] Remove admin and postgres roles

[marceloneppel]

Issue

The admin role should be removed and not available anymore to be used as an extra-user-role, as different roles were already introduced by #881 and will also be introduced by #921. Those new roles should replace the currently existing admin role.

The postgres user is not used for anything (as we have the operator user as the superuser).

Solution

Remove the admin role and the postgres user creation.

TODO: lib/charms/postgresql_k8s/v0/postgresql.py will be moved to lib/charms/postgresql_k8s/v1/postgresql.py in a next PR.

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 70.23%. Comparing base (03b7e54) to head (24605d9).
Report is 1 commits behind head on 16/edge.

Additional details and impacted files

@@             Coverage Diff             @@
##           16/edge     #931      +/-   ##
===========================================
+ Coverage    70.22%   70.23%   +0.01%     
===========================================
  Files           16       16              
  Lines         3725     3723       -2     
  Branches       542      541       -1     
===========================================
- Hits          2616     2615       -1     
  Misses         974      974              
+ Partials       135      134       -1     

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[taurus-forever]

🤞
Q: do we need to change something on pgbouncer after merging this?

[marceloneppel]

🤞 Q: do we need to change something on pgbouncer after merging this?

We'll need to update the library on PgBouncer through canonical/pgbouncer-operator#549 after merging #921, so that it properly creates the roles when a client app requests a new database to be created by PgBouncer.