kv: panic in HandleRaftUncoalescedRequest in mixed cluster

[RaduBerinde]

While working on adding 24.3 versions (#128616), I noticed the version-upgrade roachtest failing, with one node crashing here:

runtime error: index out of range [24] with length 24
*   | github.com/cockroachdb/cockroach/pkg/kv/kvserver.(*Store).HandleRaftUncoalescedRequest

Code:

	s.metrics.RaftRcvdMessages[req.Message.Type].Inc(1)

Two new message types were added after 24.2 branched in #128426

Looks like this problem is in 24.1 as well, which will be problematic in 24.1 -> 24.3 upgrades. Edit: actually, if this was true, we would have seen failures on upgrades test on master and on 24.2. To be investigated some more

Jira issue: CRDB-41178

[RaduBerinde]

The solution here might be to put the use of these new message type behind version gates (in which case we don't need to fix anything in 24.2).

[RaduBerinde]

Ok, I got to the bottom of this. #128647 added a pre-24.2 version gate to master.