[DPE-8860] config expose for postgresql-16 VM

[onkolahmet]

Added PG-16 worker process and WAL compression configuration options.

• 6 worker process settings (cpu-max-logical-replication-workers, cpu-max-parallel-apply-workers-per-subscription, cpu-max-parallel-maintenance-workers, cpu-max-parallel-workers, cpu-max-sync-workers-per-subscription, cpu-max-worker-processes)
• 1 WAL compression setting (cpu-wal-compression)
  All options support "auto" values with defaults and include descriptions for PG-16 compatibility.

[codecov]

Codecov Report

❌ Patch coverage is 91.50943% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.46%. Comparing base (451a463) to head (7127f33).
⚠️ Report is 2 commits behind head on 16/edge.

Files with missing lines	Patch %	Lines
src/charm.py	90.62%	4 Missing and 5 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           16/edge    #1284      +/-   ##
===========================================
+ Coverage    69.82%   70.46%   +0.63%     
===========================================
  Files           16       16              
  Lines         4149     4249     +100     
  Branches       658      684      +26     
===========================================
+ Hits          2897     2994      +97     
  Misses        1045     1045              
- Partials       207      210       +3     

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[marceloneppel]

@onkolahmet, please add a description to the PR. You should explain the issue and the solution. You can follow some examples from other PRs from the repo, like #1281, #1258, and #1191.

[marceloneppel]

Great job, @onkolahmet!

[marceloneppel]

LGTM!

[taurus-forever]

Thank you, Ahmet!