PR #109346 - kvcoord: Pace rangefeed client goroutine creation

[cockroach-teamcity]

Related PR: cockroachdb/cockroach#109346
Commit: cockroachdb/cockroach@8d321d4
Fixes: CRDB-25544

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Release note (enterprise change): Pace rangefeed goroutine creation
rate to improve scheduler latency. Improve observability by adding
additional column in the crdb_internal.active_rangefeed
table to indicate if the range is currently in catchup scan mode.