monitoring: annotations on all panels to see version change events of other services

[bobheadxi]

two use cases:

1. debugging if deploy of one service affects another
2. reference for services that do not export version information in metrics

e.g. postgres has alerts firing, maybe this is caused by x service rollout?

[github-actions]

Heads up @davejrt @ggilmore @dan-mckean @caugustus-sourcegraph @StephanX - the "team/delivery" label was applied to this issue.