Feature/request multiple proofs in parallel

[ARR552]

What does this PR does?

This PR adds some improvents to make the hermez node more resilient when recieves many txs. Also, now the hermez node is fast enough to full fill the baches with 2048 txs

How to test?

Tested sending 100000 txs to the hermez node. Average batch time = 66s using 3 provers

Checklist

These are the criteria that every PR should meet, please check them off as you review them:

• [ ] Include tests
• [X] Respect code style and lint
• [ ] Update swagger file (if needed)
• [ ] Update documentation (*.md) (if needed)