Today peer recovery retention leases (PRRLs) are created when starting a
replication group from scratch and during peer recovery. However, if the
replication group was migrated from nodes running a version which does not
create PRRLs (e.g. 7.3 and earlier) then it's possible that the primary was
relocated or promoted without first establishing all the expected leases.

It's not possible to establish these leases before or during primary
activation, so we must create them as soon as possible afterwards. This gives
weaker guarantees about history retention, since there's a possibility that
history will be discarded before it can be used. In practice such situations
are expected to occur only rarely.

This commit adds the machinery to create missing leases after primary
activation, and strengthens the assertions about the existence of such leases
in order to ensure that once all the leases do exist we never again enter a
state where there's a missing lease.

Relates elastic#41536

…ls-bwc-create-after-primary-activation