feature: nicer fake publish ux

[nick1udwig]

We should have more sensible defaults for fake publish. E.g. we should:

1. Not require --rpc and, if not provided, use default of ws://localhost:8545 (the default anvil),
2. If none of -k, -l, -r is provided, make a keystore for the first anvil private key & use it.

It would also be nice if we could avoid having to publish the metadata.json: that is the final annoying bit.