release-25.2: sql: automatically cleanup automatic stats jobs

[dt]

Backport 1/1 commits from #155848.

/cc @cockroachdb/release

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Automatic stats jobs are frequent -- sometimes almost continious -- background process in many clusters, constantly being created and running as part of its normal operation. In some clusters these completed jobs have been observed to make up more than 90% of the retained content of the jobs system, but in most user-visible surfaces, they are usually filtered out or excluded as they have typically been found to be of low relevance or utility to users looking for more notable, discrete cluster events tied to less continious jobs.

This change introduces automatic, immediate cleanup of automatic stats jobs so that they are eagerly removed rather than being retained for the full job retention period. This should dramatically reduce the number of these in the jobs system to just those are executing and could be relevant to the cluster's operation, and those which were manually run (and thus likely of concern to a user), as well as those which failed which could also be of interest.

Release note (ops change): successfully completed automatic SQL stats collecton jobs now automatically purged rather than being retained for the full default job retention period.
Epic: CRDB-55121.

Release justification: default-off so no behavior change unless opted-in as directed to mitigate certain production jobs system challenges.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

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[cockroach-teamcity]

This change is 

[michae2]

LGTM