kvflowcontrol,admission: use flow control during raft log catchup post node-restart

**Is your feature request related to a problem? Please describe.**

We've seen in write-heavy workloads that node restarts can result in LSM inversion due to a rapid onset of raft log catchup appends. This problem was touched on recently in https://github.com/cockroachdb/cockroach/issues/96521 + https://github.com/cockroachdb/cockroach/issues/95159 -- those issues amounted to 23.1 changes to avoid an immediate transfer of leases to newly-restarted nodes until their LSM is healthier, in order to stave off latency impact for leaseholder traffic. But it's possible to invert the LSM, which affects non-leaseholder traffic.

This issue proposes using the general flow control mechanism we're introducing in #95563 to pace the rate of catchup raft log appends to prevent LSM inversion entirely. With such a mechanism, we'd be able to transfer leases immediately to newly restarted nodes without lease-holder impact, and also avoid latency impact on follower traffic. https://github.com/cockroachdb/cockroach/issues/80607 is slightly related -- we could apply flow tokens to raft snapshots too to cover the general case of "catchup write traffic".

**Describe the solution you'd like**

https://github.com/cockroachdb/cockroach/blob/b84f10c0724f75eaf1ab00ebbcf60cd0d8607612/pkg/kv/kvserver/kvflowcontrol/doc.go#L310-L328

https://github.com/cockroachdb/cockroach/blob/b84f10c0724f75eaf1ab00ebbcf60cd0d8607612/pkg/kv/kvserver/kvflowcontrol/doc.go#L353-L375

This is also touched on here: https://reviewable.io/reviews/cockroachdb/cockroach/96642#-NOF0fl20XuBrK4Ywlzp.

Jira issue: CRDB-25460

Start with pkg/kv/kvserver/kvflowcontrol/doc.go, especially lines 310-328 and 353-375, then read the flow-control work in #95563 and the linked review discussion. The goal is to define and implement pacing for catchup raft log appends so node restarts do not cause LSM inversion; no specific implementation file or test is named.

Written by the indexing model from the issue text.