release-23.1: util/mon: add cluster setting for disabling monitor tree tracking

[yuzefovich]

Backport 1/1 commits from #121722.

/cc @cockroachdb/release

---

We already have an env var for this, but it requires a node restart to apply. Having a cluster setting will allow us to disable the monitor tree tracking without the node restart, but it might also help us prove that it's Go GC deficiency to blame for the suspected memory leak: namely, if we find a cluster that has the leak and disable the tree tracking via the cluster setting, if it's Go GC deficiency, the leak would be cleaned up; if it's CRDB memory leak, then the leak will remain but will stop growing.

Epic: None

Release note: None

Release justification: low-risk improvement.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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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?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[yuzefovich]

blathers backport release-23.1.18-rc