chore(seer-infra-telemetry): Place user-level auth monitoring connections under their own feature flag (frontend) (#123027)

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.

Redirect the connectors page (shows user-level monitoring connections)
to Seer settings if the flag is off. Put any reauth flow under the flag.

Corresponding backend PR:
https://github.com/getsentry/sentry/pull/123025


https://github.com/user-attachments/assets/a2505b32-319c-49f6-8ca0-dd36c318e27a