Mir-miner process and CLI

[adlrocha]

Create a mir-validator cli that handles all mir-specific features, and runs a Mir validator process. With this, lotus-miner will be used by SPs to handle all storage-related features (proofs, deals, etc.). While validators will have to run a mir-miner to propose and validate new blocks.

Validators initialize their own repo and run a separate libp2p-host from the daemon and the lotus-miner.

Depends on: #3

Note: We don't need to call it mir-validator, I used it in the description to clarify the purpose of the tool, but we can call plainly mir

[adlrocha]

Implemented. The code is available in the spacenet branch (new main branch of the repo). This won't be merged to lotus mater yet (at least for now).