serverutils: flake in tests that use ALTER TENANT SET CLUSTER SETTING

[knz]

Describe the problem

Found by @miretskiy in #110516:

=== RUN   TestAlterChangefeedSwitchFamily/kafka
    alter_changefeed_test.go:282: failed to start feed for job 0: pq: rangefeeds require the kv.rangefeed.enabled setting. See https://www.cockroachlabs.com/docs/v23.2/change-data-capture.html#enable-rangefeeds-to-reduce-latency

In a nutshell the test does this:

1. StartServer()
2. ALTER TENANT ALL SET CLUSTER SETTING kv.rangefeed.enabled = true via SQL
3. StartTenant()

then the error happens when the test uses the tenant service.

The problem is that the setting override at step (2) has not yet propagated through the rangefeed when StartTenant is invoked.

Expected behavior

StartTenant should also restart the rangefeed on the setting overrides (currnetly it only restarts the rangefeed on the tenant metadata and capabilities).

Jira issue: CRDB-31506
Epic: CRDB-18499

[blathers-crl]

Hi @knz, please add branch-* labels to identify which branch(es) this release-blocker affects.

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[knz]

sadly my patch didn't fully fix this.