add href to health check responses

[briantist]

Addendum to #33 adding an href field to health check responses.
This can be useful to ensure URL generation is working.
Also fixed some formatting.

cc @jcox10

[codecov]

Codecov Report

Base: 51.94% // Head: 51.77% // Decreases project coverage by -0.17% ⚠️

Coverage data is based on head (2a990b3) compared to base (0a676a5).
Patch coverage: 11.11% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #34      +/-   ##
==========================================
- Coverage   51.94%   51.77%   -0.18%     
==========================================
  Files          22       22              
  Lines         872      875       +3     
==========================================
  Hits          453      453              
- Misses        419      422       +3     

Impacted Files	Coverage Δ
galactory/api/v2/collections.py	20.75% <0.00%> (ø)
galactory/health/v1/health_checks.py	40.74% <20.00%> (-5.10%)	⬇️

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