changefeedccl: add scoped metric for catchup ranges

Right now, there exists a metric `distsender.rangefeed.catchup_ranges` that counts the number of ranges doing catchup scans, but it isn't scoped on a per-changefeed basis. We could add a new `changefeed.catchup_ranges` metric (analogous to `changefeed.lagging_ranges`) that will count that.

Jira issue: CRDB-55632

Start by locating the existing distsender.rangefeed.catchup_ranges metric and the analogous changefeed.lagging_ranges metric. Trace how those metrics are scoped and reported, then add the requested changefeed.catchup_ranges metric so it counts catchup-scanning ranges per changefeed; done means the metric is exposed with the intended scope and behavior.

Written by the indexing model from the issue text.