Proxy metric names for identity cert management are inaccurate for edge-24.5.1

[AndyJS]

After upgrading from linkerd2 edge-24.3.5 to edge-24.5.1 I've found that the following set of proxy metrics scraped from my pods have been renamed:

identity_cert_refreshes_total renamed to control_identity_cert_refreshes_total

identity_cert_refresh_timestamp_seconds renamed to control_identity_cert_refresh_timestamp_seconds

identity_cert_expiration_timestamp_seconds renamed to control_identity_cert_expiration_timestamp_seconds

I can't find the specific merge that introduced this change in prefix in the linkerd2-proxy or linkerd2 release notes, but if this was intentional the documentation will need to be updated to reflect this.

e.g.

website/linkerd.io/content/2.15/reference/proxy-metrics.md

Line 234 in eb40950

* `identity_cert_expiration_timestamp_seconds`: A gauge of the time when the