[Admittance] multiple state/command interfaces

[MarcoMagriDev]

This PR aims to address the following issues:

1. Fix wrong has flags used in write and read methods
2. Fix wrong fields of state_commanded used in write_state_to_hardware
3. Fix that multiple state interfaces are configured only the position state interface is considered due to else if statement.

Moreover:

1. Makes position state interface mandatory, otherwise the controller will not be able to perform computations. The controller will not be configured if not provided.
2. Adds compatibility with velocity command interface without position command interface.