release-23.1: sql: fix StatementStatistics.Nodes list

[j82w]

Backport 1/1 commits from #106587.

/cc @cockroachdb/release

---

1. Fixes the nodes list to show all the nodes in StatementStatistics.Nodes.
2. The node list is now empty if tracing is disabled. Previously it would always include the current gateway node id, but it would be missing all the other nodes. This causes confusion because it's uncertain whether the node list is complete or not.
3. Fixes regions on EXPLAIN ANALYSE (DISTSQL) to show regions information on secondary tenenants. It was not shown before because only system tenants have access to gossip which is used under the covers to get the node descriptors.
4. Fixes the performance issues previously listed in sqlstats: "get regions for node" logic is extremely inefficient #102170.
5. Fixes the test to actually validate the nodes list.

The fix was done by adding the region name to the Flow ComponentID. This means the region name is now part of the traces for the Flow ComponentID, so it no longer needs figure out the region. It gets the region information from the same trace the SQL Instance ID is obtained. Moving the collection to the QueryLevelStats avoids iterating the traces multiple times.

Fixes: #102170, fixes: #96647, fixes: #91219;
Epic: none
Release note (bug fix): Fixes the StatementStatistics.Nodes to
contain all the nodes involved in the query. Adds region info to
EXPLAIN ANALYSE (DISTSQL) for secondary tenants.

Release Justification: Bug fix the node and region information.

[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 

[yuzefovich]

Reviewed 18 of 18 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @rytaft)