Set participant public key during transcript aggregations

[piotr-roslaniec]

An additional idea from a discussion with @KPrasch: what a about adding the ritual public key as part of the post transcript TX?

• Piggy-backing from the post transcript TX simplifies things, maybe we can make it an optional parameter in case the the node needs to set the key. Less TXs means simpler client code, less problems.
• Prepares API for when/if Ferveo keys are generated per-ritual.
• Code definitely would look uglier, but I think this is bearable considering Coordinator is for the private beta release.

If this sounds good, we can do this in a separate PR, no need to do it here.

Originally posted by @cygnusv in #77 (review)

[cygnusv]

Closing this for the moment, as we're going to use the setting of participants' public keys as evidence of correct operator set up.

[piotr-roslaniec]

@cygnusv This was already implemented and merged in #77
The work on integrating this into nucypher continues here: nucypher/nucypher#3188

Sorry, I forgot to close this issue

[cygnusv]

My understanding is that #77 added the public key requirement as a separate TX from posting transcripts, and this issue was proposing to unify them. But after recent discussions with @vzotova, we decided to keep them separate, so that's why this issue is being closed now.