Next step in process of making BEEFY being able to generate both ECDSA
and BLS signature after #1705. It allows BEEFY to use a pair of ECDSA
and BLS key as a AuthorityId.
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Co-authored-by: Davide Galassi <davxy@datawok.net>
Co-authored-by: Robert Hambrock <roberthambrock@gmail.com>