Documentation update for end-to-end traceability of sessions

SDK

• document new timing info coming from server
• setting "slow operation" threshold on client
• setting "slow operation" threshold on server
• example of saving slow operations to client logs
• example of capturing client timing to get an overall timing of operation

kv engine

• update protocol to show timing details
• setting "slow operation" threshold on server
• show example of slow operations log (if not already doc'd)