sql,kv: permit txn rollbacks across LockNotAvailable errors

[jseldess]

Jesse Seldess commented:

PR: cockroachdb/cockroach#67514

From release notes:

ROLLBACK TO SAVEPOINT can now be used to recover from LockNotAvailable errors (pgcode 55P03), which are returned when performing a [FOR UPDATE SELECT](../v21.2/select-for-update.html] with a NOWAIT wait policy. [#67514][#67514) {% comment %}doc{% endcomment %}

Jira Issue: DOC-1391