Set correct statsd namespace for consumer arroyo metrics

[NicoHinderling]

vanity improvement :P

To match convention so our arroyo consumer metrics use the same metric name as the others

[chromy]

Lgtm, thanks!

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.78%. Comparing base (080325c) to head (ea9b131).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/launchpad/utils/arroyo_metrics.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #414   +/-   ##
=======================================
  Coverage   79.78%   79.78%           
=======================================
  Files         147      147           
  Lines       11845    11845           
  Branches     1207     1207           
=======================================
  Hits         9451     9451           
  Misses       1960     1960           
  Partials      434      434           

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