* Update recovery-internals documentation
Patch updates recovery-internals documentation to record changes
related to CC driving cluster-recovery state machine (earlier driven
by the master)
* Revert "Revert "Refactor: ClusterController driving cluster-recovery state machine""
Major changes includes:
1. Re-revert Sequencer refactor commits listed below (in listed order):
1.a. This reverts commit bb17e194d9.
1.b. This reverts commit d174bb2e06.
1.c. This reverts commit 30b05b469c.
2. Update Status.actor to track ClusterController interface to track
recovery status.
3. Introduce a ServerKnob to define "cluster recovery trace event"
prefix; for now keeping it as "Master", however, it should allow
smooth transition to "Cluster" prefix as it seems more appropriate.
The definition of knownCommittedVersion is authored by Alex Miller;
The revision on which version of data SS should revert is based on
Jingyu Zhou's review comment.
Jon Fu