Limit Cardano transactions prover input

[jpraynaud]

Why

In order to guarantee good performances of the aggregator, we need to bound the input of the prover (in particular, the number of transactions to be certified).

What

Implement a limit on the number of transactions that can be certified at once, and provide sanitation of the given input.

How

• Handle invalid hashes (return a 400 Bad request):
  • empty string
  • length != 64
  • ascii hexadecimal digit character only
  • add a maximum number of transactions to be certified at once in the prover route
• Deduplicate list of transactions
• Update the proof message returned by the route with "out of bounds" transactions (which need to be certified in a separate call, add a reason for all the non certified messages).
• Make this value a parameter of the aggregator (display it in the root route of the REST API)
• Adapt Open API specs
• Adapt explorer