kvserver: historical protected timestamp records

Removing old protected timestamps often uncorks a large GC backlog which can topple the cluster (see #82955). We have limited insight into these protected timestamp records after-the-fact. It would be helpful to keep a record of them in debug.zips and elsewhere, e.g. in `system.protected_ts_records` or logs or whatever.

We recently added time series metrics in #98540 which go some way towards this.

Jira issue: CRDB-27398