kvserver: add timeout for lease acquisitions

[lunevalex]

Lease acquisitions should have a timeout. It should be set to twice the Raft election timeout (6 seconds total), since it may need to hold a Raft election and repropose the lease acquisition command, each of which may take up to one election timeout.

Without this timeout, it's possible for a lease acquisition to stall indefinitely (e.g. in the case of a stalled disk). This prevents a
NotLeaseHolderError from being returned to the client DistSender, which in turn prevents it from trying other replicas that could acquire the lease instead. This can cause a lease to remain invalid forever.

Jira issue: CRDB-16080