release-22.1: server: react to decommissioning nodes by proactively enqueuing their replicas

[aayushshah15]

Backport 2/2 commits from #80993 and 1/1 commit from #82683.

/cc @cockroachdb/release

---

Note: This patch implements a subset of #80836

Previously, when a node was marked DECOMMISSIONING, other nodes in the
system would learn about it via gossip but wouldn't do much in the way
of reacting to it. They'd rely on their replicaScanner to gradually
run into the decommissioning node's ranges and rely on their
replicateQueue to then rebalance them.

This meant that even when decommissioning a mostly empty node, our worst
case lower bound for marking that node fully decommissioned was one
full scanner interval (which is 10 minutes by default).

This patch improves this behavior by installing an idempotent callback
that is invoked every time a node is detected to be DECOMMISSIONING.
When it is run, the callback enqueues all the replicas on the local
stores that are on ranges that also have replicas on the decommissioning
node. Note that when nodes in the system restart, they'll re-invoke this callback
for any already DECOMMISSIONING node.

Resolves #79453

Release note (performance improvement): Decommissioning should now be
substantially faster, particularly for small to moderately loaded nodes.

Release justification: non-invasive performance improvement for node decommissioning

[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 

[aayushshah15]

Don't stamp yet, there's a bug in the original patch that I need to fix first.

[aayushshah15]

@kvoli and / or @AlexTalks: could I get a stamp on this? This patch has been baking on master for over a week and we haven't seen any fallout related to it.

[kvoli]

LGTM