release-24.1: kvserver: split snapshot SSTables for mvcc keys into multiple SSTs

[itsbilal]

Backport 1/1 commits from #127997.

/cc @cockroachdb/release

Release justification: Performance improvement that has baked in master for a while, that was originally identified in a support escalation.

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Previously, we'd only create one sstable for all mvcc keys in a range when ingesting a rebalance/recovery snapshot into Pebble. This increased write-amp in Pebble as more sstables would have to be compacted into it (or the sstable then split into smaller ones in Pebble), and had other consequences such as massive filter blocks in the large singular sstable.

This change adds a new cluster setting,
kv.snapshot_rebalance.max_sst_size, that sets the max size of the sstables containing user/mvcc keys in a range. If an sstable exceeds this size in multiSSTWriter, we roll over that sstable and create a new one.

Epic: CRDB-8471
Fixes: #67284

Release note (performance improvement): Reduce the write-amplification impact of rebalances by splitting snapshot sstable files into smaller ones before ingesting them into Pebble.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
• Backports should not break backwards-compatibility.
• Backports should change as little code as possible.
• Backports should not change on-disk formats or node communication protocols.
• Backports should not add new functionality (except as defined
  here).
• Backports must not add, edit, or otherwise modify cluster versions; or add version gates.
• All backports must be reviewed by the owning areas TL. For more information as to how that review should be conducted, please consult the backport
  policy.

If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• 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. State changes must be further protected such that nodes running old binaries will not be negatively impacted by the new state (with a mixed version test added).
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.
• Your backport must be accompanied by a post to the appropriate Slack
  channel (#db-backports-point-releases or #db-backports-XX-X-release) for awareness and discussion.

Also, please add a brief release justification to the body of your PR to justify this
backport.

[cockroach-teamcity]

This change is 

[itsbilal]

This wouldn't compile until the Fragmenter and MakeInternalKeyTrailer are exported from Pebble, which I'll do momentarily.

[jbowens]

Noting that we'll need the eventual fix to #129026 before merging any backport. I think regardless, we'll want it to bake on master for a while.

[itsbilal]

Backported #129088. This should be ready for another look.

[itsbilal]

TFTR!