[DPE-8005] Handle empty region

[dragomirp]

Port of canonical/postgresql-operator#1117, canonical/postgresql-operator#1149 and canonical/postgresql-operator#1154 for 14/edge k8s:

• Handle empty region when creating backups
• Handle invalid stanza name in Pgbackrest output (happens when no region is set in GCP) to block as failure to initialise stanza and not as foreign backup
• Add ceph test

Checklist

• I have added or updated any relevant documentation.
• I have cleaned any remaining cloud resources from my accounts.

[codecov]

Codecov Report

❌ Patch coverage is 76.19048% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.22%. Comparing base (bee017f) to head (ec73e2f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/backups.py	76.19%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1100      +/-   ##
==========================================
- Coverage   73.27%   73.22%   -0.06%     
==========================================
  Files          15       15              
  Lines        3922     3929       +7     
  Branches      575      577       +2     
==========================================
+ Hits         2874     2877       +3     
- Misses        834      836       +2     
- Partials      214      216       +2     

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