Implement KeyManager API to be able to integrate to EthDocker

[Arkenan]

https://ethereum.github.io/keymanager-APIs/#/

• Implement Local Key Manager set of endpoints #1256
• Implement Fee Recipient set of endpoints #1257
• Implement Gas Limit set of endpoints #1258
• Implement Remote Key Manager set of endpoints  #1259
• Use a secure channel for serving the validator API #1260
• Handle Keystore query timeouts during sync in Libp2pPort #1261
• [Validator API] Improve response messages #1262
• [Validator API] Add first validator #1263
• [Validator API] Handle repeated validators #1264
• [Validator API] Add unit tests #1265
• [Validator API] Add slashing protection #1267
• [Validator API] Handle bad requests #1268
• Support kdf paths on Keystore #1030
• Handle keys with no deposits #1269