release-24.2: roachtest: wait for propagation of tenant cluster settings

[blathers-crl]

Backport 1/1 commits from #137843 on behalf of @nvanbenschoten.

/cc @cockroachdb/release

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Fixes #137503.

This commit updates the setTenantSetting utility to wait for the propagation of the tenant cluster settings to each SQL gateway before returning. This avoids races where the tenant cluster settings are not yet propagated to the SQL gateway when the test randomly chooses a gateway and tries to use it.

Release note: None

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
• Backports should not break backwards-compatibility.
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  here).
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If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
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backport.

[cockroach-teamcity]

This change is