deprecate recommender_v1 endpoint

[alexskr]

Deprecate unused /recommender_v1 endpoint.

• respond with 410 Gone status.
• add a reminder to completely remove this in 1 year

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.33%. Comparing base (c2f1c58) to head (f089e32).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #166      +/-   ##
===========================================
- Coverage    73.39%   73.33%   -0.06%     
===========================================
  Files           53       53              
  Lines         2954     2948       -6     
===========================================
- Hits          2168     2162       -6     
  Misses         786      786              

Flag	Coverage Δ
unittests	73.33% <100.00%> (-0.06%)	⬇️

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