Allow optimistic lock in POST (update) API for previous version check

[neeraj9]

At present the APIs for both details and links overwrite the existing content unconditionally. This strategy might seem useful for most of the cases, but there are situations when application wants to validate against the version it read before making that change. This optimistic lock by application will give more control towards maintaining consistency in the event of simultaneous writes.

This has direct impact on indexing when the new content has index changes.
Since there is no mechanism to allow rollback, so it is tricky how this lock
will be eventually implemented. Note that any change in indexes is executed first
before making change to the detail information. Having said that in case of failure
to update due to optimistic lock would break indexes and would not be possible
for a rollback.