storage: add comment to replicaGC with pending split

Persists a recent finding I made experimenting with cockroachdb#32594.

Release note: None

pkg/storage/replica_gc_queue.go

@@ -264,6 +264,14 @@ func (rgcq *replicaGCQueue) process(
  // look it up by RangeID) to disable the mechanism in #31875 for it.
  // We should be able to use prefetching unconditionally to have this
  // desc ready whenever we need it.
+ //
+ // NB: there's solid evidence that this phenomenon can actually lead
+ // to a large spike in Raft snapshots early in the life of a cluster
+ // (in particular when combined with a restore operation) when the
+ // removed replica has many pending splits and thus incurs a Raft
+ // snapshot for *each* of them. This typically happens for the last
+ // range:
+ // [n1,replicaGC,s1,r33/1:/{Table/53/1/3…-Max}] removing replica [...]
  log.Infof(ctx, "removing replica with pending split; will incur Raft snapshot for right hand side")
  }