[FEAT] Generate some empty blocks to make era-test-node work nicer with wallets like metamask

[mm-zk]

🌟 Feature Request

📝 Description

If you use your metamask wallet with era-test-node, the transactions might show up as 'pending'.
This is due to the fact that era-test-node is generating new blocks only when a new transaction shows up, and meta-mask is waiting (by default) for the next block before even checking if transaction was executed.

There are 2 solutions:

• have era-test-node generate a block every couple seconds - it is simple solution, but will create potentially a bunch of noise in the logs etc.
• or - have era-test-node create an empty block after couple seconds, only if the previous block was non-empty - while this is a little bit more complex, it means that if you send a transaction (and then do nothing), test node would still generate an empty block, which should help wallets like metamask to correctly mark the transaction as completed.

[MexicanAce]

I think this would require support of something like Mining Modes from Hardhat.

My preference would be to keep things simple and go with the first option: generate a block every couple of seconds and make this optional while keeping the noise in the logs to a minimum