sequencer, mempool: add grpc queries to get transaction status

[Lilyjjo]

Right now we don't have a good way for users to query the status of a transaction. It would be a nice UX if users could get information on where their transaction is and why.

Possible transaction states and responses:

• Executed
  • return block number which transaction executed in
• In pending
  • return pending and other info about other transactions in pending
• In parked
  • return why in parked and info about other transactions in parked
• Failed
  • return why failed

┆Issue Number: ENG-973