[DPE-5833] Create new PostgreSQL version 16 charm

[lucasgameiroborges]

Part of the 4-PR bundle to merge PostgreSQL 16. See doc for further info: https://docs.google.com/document/d/1K4xMxKDOiHfdCTc_hxMh6bW1DCZ6HC6wa6g8tAJAtno/edit?tab=t.0

[codecov]

Codecov Report

Attention: Patch coverage is 45.45455% with 6 lines in your changes missing coverage. Please review.

Project coverage is 71.81%. Comparing base (5dd067f) to head (e41d396).

Files with missing lines	Patch %	Lines
src/charm.py	40.00%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           16/edge     #680      +/-   ##
===========================================
- Coverage    71.92%   71.81%   -0.11%     
===========================================
  Files           15       15              
  Lines         3476     3484       +8     
  Branches       535      537       +2     
===========================================
+ Hits          2500     2502       +2     
- Misses         845      850       +5     
- Partials       131      132       +1     

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