feat(split): add split_status

[hycdong]

This pull request adds two sturctures to show split status.

split_status (in replication.thirft)

Define five split_status for partition (not_split, splitting, pausing, paused, canceling), both replica and meta will use it.

• For replica, we used to use _child_gpid to distinguish whether a replica is executing splitting, if _child_gpid.get_app_id() > 0, the replica is splitting, otherwise not. It can only show two split status. Now, we use _split_status to describe partition split status.
• For meta, see split_state

split_state (in meta_data.h)

Define sturct split_state to show app split progress, this sturcture include splitting partition count and each split_status for those splitting partitions. If splitting_count = 0, it means current app is not splitting or has finished splitting.

This sturcture is helpful to query app split progress and easier to understand. In previous implementation, when an app is executing splitting, tha ballot of not-ready child partition is invalid_ballot( < 0), so we should traverse app->partitions to check if any partition whose ballot is invalid. Now, we just check the value of splitting_count.

This pr also update related unit tests.

[foreverneverer]

The file seem not be named xxxmanager, since it does not any manager work, may you can named better name later