Manage ethereum based identities

[daveroga]

• Manage ethereum based identities.

1. Implement create method.
   a. add bjj key Auth credential.
   b. first state transtition must be mandatory after adding the Auth credential.
2. Implement state transition for ethereum identities. (transitState / transitStateGeneric)
3. Test flow when ethereum based identity is an issuer.

• Fix for sec256k1 when private key generation is less than 32 bytes in hex representation

Review

1. We need to sign a new auth bjj key with old one (e.g. k2 with k1). If there is no k1 and state is genesis - we can add MTP as now.
2. For ethereum identity and for k2 we can add Iden3SparseMerkeTreeProof after the state transition.
3. Write some tests for key rotation / adding new keys.

[Kolezhniuk]

Please merge latest develop and make sure that tests points to Amoy network