* Adds MerkleLogConfirm &Adds MerkleLogConfirmMessage
* Adds MerkleLogUnequivocal & MerkleLogUnequivocalMessage (currently
  empty, just claims the pb ordinals we know we will need)
* Removes MerkleLogCommitMongoDB
* Removes log version, log epoch and massif index. All of which
  are harmful to our strategy for managing the backing storage.
  See
  https://github.com/datatrails/
   epic-8120-scalable-proof-mechanisms/
   blob/e38ca5e050356a47028b1d2b47bb6f02ff6c5c3c/mmr/
   forestrie-mmrblobs.md#changing-the-massifheight-for-a-log
  for important context
* Adds EventResponseJSONAPI, which largely duplicates EventResponse but
  importantly, supports decoding the format the *customer* will see from
  our apis. The duplication is unfortunate, but it means we can stop
  having ad-hoc soultions to this problem in all our go-lang based demo
  code. It also means the data can be reliably decoded with protojson.
  the generic json unmarshal fails to deal with 64 bit unsigned integers
  (and other numbers) correctly for example.

Put EventResponseJSONAPI in its own file

And add appropriate file comments for both eventresponse.proto and
eventresponsejsonapi.proto

AB#8336