storage: force new lease sequence number after restart

While we were already making sure that a lease obtained before a node
restart was not used after, the new requested lease would usually be an
extension of the old. As such, commands proposed under both would be
able to apply under the new one, which could theoretically cause
consistency issues as the previous commands would not be tracked by the
command queue (though it would be hard to engineer and has not been
observed in practice, to the best of our knowledge).

This change plugs that hole by preventing an extension of a previously
held lease post restart.

Touches cockroachdb#10420.

Release note (bug fix): Prevent potential consistency issues when a node
is stopped and restarted in rapid succession.