Allow relayers to report signers?

[HCastano]

Follow up from #1215. Right now signers have the ability to report other signers for
unresponsiveness/offine behaviour. One question that came up during #1215 was whether or
not to allow relayers, whose role it is to forward messages to signers, to report in the
case a signer doesn't accept their relayed messages.

I'm thinking that we initially disallow it to focus on the signer-to-signer interactions.
We can always lift this restriction later.

[ameba23]

Since the really dangerous attacks involve a malicious actor controlling the majority of the signer set, i think its important that non-signers have the ability to report signers misbehaving.