Document newly-added wall clock times to ReplSetGetStatus command

Description

As of SERVER-40353, SERVER-40078, and SERVER-40080, wall clock times have been added corresponding to the various optimes in the ReplSetGetStatus optimes subdocument. The umbrella ticket for these changes is SERVER-34598. These new wall clock times should be documented.

Scope of changes

optimes

• lastCommittedWallTime (SERVER-40078)
• readConcernMajorityWallTime (SERVER-40353)
• lastAppliedWallTime (SERVER-40080)
• lastDurableWallTime (SERVER-40080)

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)