clean up responsibilities of {process,apply}RaftCommand
clean up responsibilities of {process,apply}RaftCommand

address @bdarnell's comments, in particular

- proposeRaftCommand will *always* call applyRaftCommand
- applyRaftCommand
  - checks leader lease of proposer (with correct response cache handling)
  - resolves intents asynchronously
  - **always** advances applied index
  - if anything goes wrong: replicaCorruption

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zes/cockroach,petermattis/cockroach,chrisseto/cockroach,fengshao0907/cockroach,jamesgraves/cockroach,vivekmenezes/cockroach,abhishekgahlot/cockroach,il9ue/cockroach,nieyy/cockroach,jgautheron/cockroach,cockroachdb/cockroach,loucash/cockroach,yosiat/cockroach,mbertschler/cockroach,vivekmenezes/cockroach,vaibhavarora/cockroach,marcuswestin/cockroach,hassyma/cockroach,chrisseto/cockroach,Abioy/cockroach,cuongdo/cockroach,jgautheron/cockroach,cuongdo/cockroach,il9ue/cockroach,SustainFund/cockroach,arjun4084346/cockroach,jess-edwards/cockroach,cuongdo/cockroach,briceburg/cockroach,veteranlu/cockroach,il9ue/cockroach,jess-edwards/cockroach,fengshao0907/cockroach,yosiat/cockroach,arjun4084346/cockroach