sql: provide session variable to allow for FOR UPDATE locks to be replicated

[ajwerner]

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

This tracks the idea that in some cases, it is desirable for FOR UPDATE locks to be durable. This will reduce the chance for a client to unknowingly lose a lock (though it will not fully eliminate that chance if either the transaction coordinator or the client itself is partitioned or aborted, perhaps due to deadlock or a higher-priority pusher).

Describe the solution you'd like
Add a session variable which allows FOR UPDATE locks to lead to a durable lock being replicated.

Additional context
There are a few problems with this:

1. We already don't wait for replication in the common case because we find transaction pipelining is important
2. Work to buffer writes is going to avoid replicating locks (IIUC).

Jira issue: CRDB-20123

[nvanbenschoten]

Replacing with #100193, which is a more general issue describing the same ask.