kvserver: no raft snaps should be necessary without log truncations

[tbg]

See #87554 for discussion.

It should always be possible to add a voter without relying on the raft snapshot queue, assuming log truncations are disabled.

We're seeing that this isn't true, but only due to inefficiencies in the implementation.

This comment motivates and makes two suggestions:

• address a TODO in raft to move out of StateSnap more freely
• also probe followers in StateSnapshot

Together they should achieve the stated goal, which the test in #87554 can help verify.

Jira issue: CRDB-23999

Epic CRDB-39898

[blathers-crl]

cc @cockroachdb/replication

[andrewbaptist]

Is this something that is likely to get into 23.1? It doesn't have any release/ga blocker tags on it? If you do I will wait on my TestDelegateSnapshot test #96841 and unskip it once this is fixed. Otherwise, I can look at alternatives to make that less flakey with the current behavior.
Thanks!

[tbg]

Is this something that is likely to get into 23.1?

Sorry, missed this until just now. No, we're not going to get this into 23.1, apologies.