chore: seed: add cmd for adding signers to rkh to genesis

[jennijuju]

Proposed Changes

currently, following this guide to spin up a local testnet doesn't give the dev control over the verifreg.
adding the below command, where dev can specify the signers, they'd like to have for verifreg upon genesis creation. the command also allocate some FIL to the signer account so it easier to test operation later.

./lotus-seed genesis add-signers --threshold=<>  --signers <pubkey1> --signers <pubkey2> localnet.json

Additional Info

Checklist

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