Automatically fill `--announce` flag on filc `deal` subcommand

[elijaharita]

When the boost PR merges, filc users will need to fill the --announce flag with /ip4/[public ip]/tcp/6755 when making deals. This is pretty un-discoverable for general users, and I don't think there's any reason not to just abstract this away in most cases.

It's fine just to do this at the filc level. This feature is mainly for CLI accessibility. The main filclient library can continue to require this field.