Add keys endpoint

[dominic22]

Remove identity.rs dependency from the audit-trail-gw and query the keys from the ssi-bridge which needs to implement an endpoint to do so.

// TODO replace this with a new endpoint at the ssi-bridge
const keypair = new Identity.KeyPair(Identity.KeyType.X25519);

• add endpoint GET /identities/create-keys
  • params: key-type enum with values ed25519 or x25519
• query the keys from the audit-trail-gw instead of using the line shown above.
• add to swagger docs
• add some tests
• remove dependency to identity.rs-wasm from audit-trail-gw