Migrate from New Relic go-agent v2 to v3

[AmanGIT07]

pkg/db/db.go and internal/store/spicedb/relation_repository.go import the deprecated github.com/newrelic/go-agent v2 package. Migrate to v3: new import path and the reworked transaction/segment APIs at every telemetry call site.

Part of #1782.

[ravisuhag]

@AmanGIT07 we can move away from new relic to open telemetry.

[AmanGIT07]

Noted, will check it out @ravisuhag