dev(rate-limits): Increase backfill query allocation to 60 per s

[jangjodi]

Based on the Datadog metrics and the corresponding Sentry error, the getsentry.tasks.backfill_grouping_records referrer is hitting our 30/s rate limit pretty frequently.

We would like to increase to 60/s if okay with team. The queries that we're making are point queries, so they should not scan very much data.