Implement Push Auth support for 2FA verification

When 2fa_verify command is executed:

• A user is asked to enter OTP
• A blocking call for push auth is performed

Then:

• If the push auth request fails, the user is still able to enter OTP
• If OTP is invalid, the 2fa_verify command ends the execution
• If OTP is valid or push auth request succeeded, then the user is successfully authenticated
• If 30 seconds passed while no OTP or Push have been provided, then the 2fa_verify command ends the execution

Closes #506 (closed)