Restart DB process test

[marceloneppel]

Issue

• Jira issues: DPE-542
• The PostgreSQL charm should self heal the workload when restarting the DB process.

Solution

• Add a test that restarts the DB processes (from Patroni and from PostgreSQL) and later check that the workload recovers itself from that situation.

Context

• This test can also be run on an existing cluster.

Testing

• The test was added on tests/integration/ha_tests/test_self_healing.py. The test restarts both Patroni and PostgreSQL OS process, one at a time.

Release Notes

• Add restart db process test.

[codecov]

Codecov Report

Merging #46 (62ada2d) into main (4994516) will increase coverage by 1.60%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
+ Coverage   62.45%   64.05%   +1.60%     
==========================================
  Files           6        6              
  Lines         815      818       +3     
  Branches      122      121       -1     
==========================================
+ Hits          509      524      +15     
+ Misses        276      264      -12     
  Partials       30       30              

Impacted Files	Coverage Δ
src/charm.py	56.25% <0.00%> (+2.99%)	⬆️

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