Unify entity version and name validation

[CasperWA]

Fixes #90

The entity version and name validation is unified to be located mainly in the models module, then from there being used in the service - instead of the service having its own special validation implementation.

Note: There's a lot of code duplication in this PR, but this will be remedied by #74.

[codecov]

Codecov Report

Attention: Patch coverage is 72.22222% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 90.06%. Comparing base (b2beefc) to head (36f2613).

Files	Patch %	Lines
entities_service/models/soft.py	70.58%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #91      +/-   ##
==========================================
- Coverage   90.77%   90.06%   -0.72%     
==========================================
  Files          21       21              
  Lines         954      986      +32     
==========================================
+ Hits          866      888      +22     
- Misses         88       98      +10     

Flag	Coverage Δ
docker	70.58% <72.22%> (-0.07%)	⬇️
local	88.74% <72.22%> (-0.68%)	⬇️

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