chore(seer-infra-telemetry): Place user-level auth monitoring connections under their own feature flag (backend) (#123025)

Fixes CW-1966

In prep for rollout, we are going to be using org-level auth
connections. Let's put the user-level auth connections under their own
feature flag `organizations:seer-infra-telemetry-user-level-auth` to be
turned off, with `organizations:seer-infra-telemetry` remaining as the
master killswitch.

Corresponding frontend PR:
https://github.com/getsentry/sentry/pull/123027