[UX] Grey out the number of shares for each signer during MuSig2 group creation

[SPXcz]

As MuSig2 is an n-out-of-n scheme, all signers need to sign a message to generate a valid signature. Therefore there is no use case for the user to own more than one secret share. The user should not be able to select the number of shares in the group creation menu. Each signer in the group should own exactly one share.

As a user, I might want to save one share in the client and one share on the card but this out of high level design scope of MeeSign.

Reference screenshot:

[quapka]

Good catch, thanks. Either grey out or possibly remove the < and > altogether for Musig2. What do you think, @Ojin13?