release-21.2: sql: add ALTER RANGE RELOCATE

[lunevalex]

Backport 1/1 commits from #72305.

/cc @cockroachdb/release

---

This commit introduces a new ALTER RANGE RELOCATE
command, which will allow an admin to move a lease
or replica for a specific range. Unlike ALTER TABLE RELOCATE
this command works on a range_id, which makes it a lot easier
to use since the user does not have to worry about range keys, which
are difficult to deal with in an emergncy situation.

Release note (sql change): Introduce new SQL syntax ALTER RANGE RELOCATE
to move a lease or replica between stores. This is helpful in an emergency
situation to relocate data in the cluster.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• 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 

[knz]

did you not want to embark #73807 with this backport as well?

[lunevalex]

did you not want to embark #73807 with this backport as well?

Yes we probably want to backport that too, let me get this one stable and i'll open that one as well.

[rafiss]

this is stale, and there won't be any more 21.2 releases; closing