Secure authentication

[tomastiminskas]

Implement the new secure authentication we did on kotlin android that uses:

• New endpoint to get relay transport key and store it on app encrypted storage
• New endpoint to create/get hmac-key so it can be used to sign requests
• x-tranport-key from relay and send x-transport-token on each request instead of X-User-Token
• hmac-key with a signature of each request raw body so it can be verify in relay to prevent MITM attach