Deprecate AddScraper and introduce more explicit AddMetricsScraper

[dmathieu]

This is meant to go alongside #14427
If we will have AddProfilesScraper, using AddMetricsScraper makes more sense than the slightly obscure AddScraper.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.81%. Comparing base (6507ad0) to head (c184cb1).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
scraper/scraperhelper/controller.go	33.33%	2 Missing ⚠️

❌ Your patch status has failed because the patch coverage (33.33%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14428      +/-   ##
==========================================
- Coverage   91.81%   91.81%   -0.01%     
==========================================
  Files         677      677              
  Lines       42608    42610       +2     
==========================================
  Hits        39122    39122              
- Misses       2425     2427       +2     
  Partials     1061     1061              

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[songy23]

contrib tests are due to #14248