Sign concatenation of public and notif keypairs using private key of public identity

Summary: This differential implements creating as passing a signature of concatenated olm identity keys to JS.

Test Plan: Modify any place in JS where CommCoreModule.initializeCryptoAccount is called, by loggind ed25519Signature.

Reviewers: tomek, atul, bartek, kamil

Reviewed By: atul

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D6822