[Backend] Define swagger contract and create back implementation for Reset Password

[brauliodiez]

This end point should:

• Receive an userId as input param.
• Create a new temporary password
• Return then new password.

Steps:

• Define the swagger contract.
• Implement the node solution.
• Implement the mock server solution

TODO: Once we have the login implemented we will perform a check if the user is Admin and has permission to peform this operation (define a separate case for this).

Ask @manudous about this