release-23.2: kvcoord: Reintroduce catchup scan semaphore for regular rangefeed

[blathers-crl]

Backport 1/1 commits from #113966 on behalf of @miretskiy.

/cc @cockroachdb/release

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Re-introduce catchup scan semaphore limit, removed by #110919, for regular rangefeed. This hard limit on the number of catchup scans is necessary to avoid OOMs when handling large scan rangefeeds (large fan-in factor) when executing many non-local ranges.

Fixes #113489

Release note: None

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Release justification: quality/stability fix -- bring back old limiter, required to avoid OOMs.

[blathers-crl]

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[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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[cockroach-teamcity]

This change is 

[nicktrav]

EM approval ✅