Promote MCPRegistry feature

[dmartinol]

Fixes #2058

• Removed references experimental feature in docs
• Removed feature flag check in code (and test code)
• Kept references to ENABLE_EXPERIMENTAL_FEATURES in deployment tasks and manifests, and to operator.features.experimental in chart values to be reused for the next experimental feature. If we think it's not the case for now, I will remove them

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.88%. Comparing base (866b10d) to head (f1f92dd).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/thv-operator/main.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2136      +/-   ##
==========================================
+ Coverage   48.82%   48.88%   +0.06%     
==========================================
  Files         242      242              
  Lines       30714    30713       -1     
==========================================
+ Hits        14996    15015      +19     
+ Misses      14596    14573      -23     
- Partials     1122     1125       +3     

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