When a tablet is migrated and cleaned up, deallocate the tablet storage
group state on `end_migration` stage, instead of `cleanup` stage:
* When the stage is updated from `cleanup` to `end_migration`, the
storage group is removed on the leaving replica.
* When the table is initialized, if the tablet stage is `end_migration`
then we don't allocate a storage group for it. This happens for
example if the leaving replica is restarted during tablet migration.
If it's initialized in `cleanup` stage then we allocate a storage
group, and it will be deallocated when transitioning to
`end_migration`.
This guarantees that the storage group is always deallocated on the
leaving replica by `end_migration`, and that it is always allocated if
the tablet wasn't cleaned up fully yet.
It is a similar case also for the pending replica when the migration is
aborted. We deallocate the state on `revert_migration` which is the
stage following `cleanup_target`.
Previously the storage group would be allocated when the tablet is
initialized on any of the tablet replicas - also on the leaving replica,
and when the tablet stage is `cleanup` or `end_migration`, and
deallocated during `cleanup`.
This fixes the following issue:
1. A migrating tablet enters cleanup stage
2. the tablet is cleaned up successfuly
3. The leaving replica is restarted, and allocates storage group
4. tablet cleanup is not called because it was already cleaned up
4. the storage group remains allocated on the leaving replica after the
migration is completed - it's not cleaned up properly.
Fixesscylladb/scylladb#23481
(cherry picked from commit 34f15ca871)
c11a2e2aaf