Support YAML files

[gipert]

• A database can be now composed either by JSON or YAML files (or a mix)
• Refactored the code such that it will be easy to support additional file types in the future
• JsonDB has been renamed to TextDB. JsonDB still usable but a deprecation warning will be emitted

[codecov]

Codecov Report

Attention: 28 lines in your changes are missing coverage. Please review.

Comparison is base (3ad061a) 72.60% compared to head (82e1d02) 73.22%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/legendmeta/police.py	11.76%	15 Missing ⚠️
src/legendmeta/textdb.py	81.25%	9 Missing ⚠️
src/legendmeta/catalog.py	75.00%	2 Missing ⚠️
src/legendmeta/utils.py	88.88%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #49      +/-   ##
==========================================
+ Coverage   72.60%   73.22%   +0.61%     
==========================================
  Files           7        8       +1     
  Lines         741      773      +32     
==========================================
+ Hits          538      566      +28     
- Misses        203      207       +4     

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