The "announce references" command does only take a repository ID, and
carries the implicit assumption that the namespace with the same public
key as the Node ID of the receiving `radicle-node` process should be
announced, but no other namespace.
In the spirit of separating user and node identity, relax this, so that
the command also carries the public keys for which the announcement
should be made. This allows to announce arbitrary namespaces out of
storage via command.
For now, this feature is not exposed to the CLI, but rather:
- `rad sync` always announce for the public key of the active profile.
- `git-remote-rad` ditto, as it calls the same codepath.
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