Support consistent read with log-id

[drmingdrmer]

One potential solution is to use the raft-log-id as a pseudo time. This solution involves:

• Returning the log id i to the writer W when a log is applied.
• A subsequent reader R (whether it's the same as W or not) forwards i to an Openraft node for reading, Openraft will not process this read request until it has applied i.

Since the committed log id ((term, index)) in raft is monotonic, it can be used as a measure of time. However, this solution requires the application to track the log-id amount across a cluster.

Originally posted by @drmingdrmer in #262 (comment)

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[drmingdrmer]

There is nothing to be done inside OpenRaft for this feature.
The application can just wait for a specific log id to be applied with Raft::wait() and the read from the state machine.