Evaluate endpoint `Repositories::GitHttpController#info_refs` default urgency, given high traffic share (8%)

Part of #2026 (closed)

The endpoint currently has an urgency set to default (target duration 1s):

total	over low (5s)	over medium (0.5s)	over default (1s)
994,611,634	18,588	4,109,966	735,383
error budget	0.9999813313	0.9958721893	0.9992614241

(source https://log.gprd.gitlab.net/goto/2e5943f0-bce8-11ed-85ed-e7557b0a598c)

The logs show a high db_duration_s and db_replica_duration_s: https://log.gprd.gitlab.net/goto/166b02d0-bd18-11ed-85ed-e7557b0a598c