adds MergePodTemplateSpecs that merges podTemplateSpecs

[ChrisJBurns]

In future we want to be able to merge the default podTemplateSpec and the user provided podTemplateSpec for an MCPRegistry. This PR adds a MergePodTemplateSpecs function that merges a user provided and default podTemplateSpec choosing the user provided one as a preference

[codecov]

Codecov Report

❌ Patch coverage is 73.88060% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.36%. Comparing base (e724609) to head (0fc4fb0).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...md/thv-operator/pkg/registryapi/podtemplatespec.go	73.88%	31 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2770      +/-   ##
==========================================
+ Coverage   56.29%   56.36%   +0.07%     
==========================================
  Files         319      319              
  Lines       30753    30887     +134     
==========================================
+ Hits        17312    17411      +99     
- Misses      11953    11984      +31     
- Partials     1488     1492       +4     

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[dmartinol]

Could you pls link the associated story/issue?