Ed25519 signer implementation

[bestbeforetoday]

As an application developer
I want to use an Ed25519 private key to sign messages
So that I can use a widely adopted alternative to NIST P curve keys

Relates to PR hyperledger/fabric#3343

Libraries providing ed25519 support:

• Go: https://pkg.go.dev/crypto/ed25519
• Node: https://github.com/paulmillr/noble-curves
• Java: https://www.bouncycastle.org/docs/docs1.8on/org/bouncycastle/crypto/signers/Ed25519Signer.html (as a provider using standard Java security APIs)

Note that ed25519 signing implementations typically includes hashing of the message as part of the signing process. Where this is the case, the client should be configured with a hash function that simply returns the message bytes, and this needs to be clearly described in documentation.

Tasks:

• Go support for ed25519 private keys in identity.NewPrivateKeySign(), with unit tests.
• Node support for ed25519 private keys in signers.newPrivateKeySigner(), with unit tests.
• Java support for ed25519 private keys in Signers.newPrivateKeySigner(), with unit tests.