PR #103592 - security: add a cache to store client cert expirations for users

Exalate commented:

Related PR: https://github.com/cockroachdb/cockroach/pull/103592
Commit: https://github.com/cockroachdb/cockroach/commit/abdaefa02ca12d6609ec24ea558c5ddbf7677163
Fixes: CRDB-26585

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Release note (security update): There is a new
`server.client_cert_expiration_cache.capacity` setting which,
when set to a non-zero number, makes it so that the minimum
time-until-expiration of the set of client certificates seen
is stored (for every user). This setting can be used to
ensure client cert expirations are exported as a metric (if
set to zero, the metric `security.certificate.expiration.client`
will have a value of zero.

Jira Issue: DOC-7810