pageserver: investigate baseline 10-316 tenants or timelines without fresh enough metrics

[koivunej]

Earlier investigation with evidence: https://neondb.slack.com/archives/C04ESKALJB1/p1696242392749039

We should have a baseline of 0 tenants or timelines without fresh enough metrics.

Possible causes:

• sampling:
  • we send every 10min and calculate synthetic size every 10min
  • to get on the linked charts by being over 15min late (assumption)

Metric ideas:

• first collection of a new tenant from it's creation (creates, attaches)

[jcsp]

Stale