metrics: Indicate which user used legacy_api_key_v2 #3069

Job	Run time
Build backend e2e test image	2m 1s
Build frontend e2e test image	3m 35s
lint_core	14s
Build frontend unit test image	1m 18s
Lint mwdb-core web sources	46s
Build mwdb-core core image	2m 4s
Build mwdb-core web image	40s
Perform frontend unit tests	31s
Perform backend e2e tests	4m 10s
Perform frontend e2e tests	4m 1s
Push test images on Docker Hub	0s
Push images on Docker Hub	0s
	19m 20s

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