[DPE-5913] Add tls and tls-ca fields to relation databag

[lucasgameiroborges]

Identical port of canonical/postgresql-k8s-operator#719

testing

Used the reproducing steps from the previous PR: canonical/postgresql-k8s-operator#719 (comment)

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 6 lines in your changes missing coverage. Please review.

Project coverage is 71.31%. Comparing base (c5c916d) to head (e4ba15d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/relations/postgresql_provider.py	50.00%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #666      +/-   ##
==========================================
- Coverage   71.37%   71.31%   -0.07%     
==========================================
  Files          13       13              
  Lines        3179     3193      +14     
  Branches      473      476       +3     
==========================================
+ Hits         2269     2277       +8     
- Misses        796      800       +4     
- Partials      114      116       +2     

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