release-21.2: sql: support for temporary table clean up for tenants

[fqazi]

Backport 1/2 commits from #69486.

/cc @cockroachdb/release

Fixes #67401

---

Fixes: #67401
Previously, the temporary table clean-up did not execute for
tenants. This was inadequate that temporary tables would last
longer than the life span of user sessions. To address this,
this patch adds support for cleaning up on a single tenant
pod. Specifically removing checks for meta1 lease when under
a tenant, and support for listing sessions.

Release justification: low risk and fixes a tenant-related bug
Release note (bug fix): Temporary tables were not properly cleaned up for
tenants.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• 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).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[ajwerner]

Reviewable status: complete! 1 of 0 LGTMs obtained

[maryliag]

@fqazi any reason why this backport is just for one of the commits on the PR? One backport we're trying to put in is dependent on some functions you added on the other commit not included on this backport

[fqazi]

@fqazi any reason why this backport is just for one of the commits on the PR? One backport we're trying to put in is dependent on some functions you added on the other commit not included on this backport

@maryliag It was intentional because 21.2 did not support tenants across multiple pods. So, we can get away with the first commit, which was a simpler fix. The second commit took the fix further and added RPC logic to support multiple pods.