[DPE-3882] Simple speedup bootstrap

[marceloneppel]

Issue

The PostgreSQL charm takes 9-10 minutes to start (be in an Active state).

Solution

• Avoid the legacy upgrade code execution during the start process (because it's not needed while Patroni is still offline).
• Set the primary status message earlier.
• Add some debug logs of the time spent since the charm started until it reaches the Active state.
• Enabled and fixed a hidden unit test (test_set_primary_status_message). It was not being executed because of indentation in the test function.

Debug logs when using this PR charm (4 minutes and 28 seconds from the beginning of the install hook until the workload is ready):

unit-postgresql-0: 20:28:18 DEBUG unit.postgresql/0.juju-log Install start time: 2024-06-24 20:28:18.945034
...
unit-postgresql-0: 20:32:46 DEBUG unit.postgresql/0.juju-log Active workload time: 2024-06-24 20:32:46.024307

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.78%. Comparing base (dbd46b5) to head (7ce1eab).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #508      +/-   ##
==========================================
+ Coverage   69.21%   69.78%   +0.56%     
==========================================
  Files          11       11              
  Lines        2865     2866       +1     
  Branches      507      507              
==========================================
+ Hits         1983     2000      +17     
+ Misses        781      761      -20     
- Partials      101      105       +4     

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[taurus-forever]

Closed as duplicate of already merged #413
CC: @marceloneppel