Beckhoff/TC: add "adhoc ADS var" get/set

As a user I would like to be able to get/set adhoc ADS variables from IBEX.

this might be possible with adsDriver but may need some experimentation to see if it's possible at all as the asyn call will need to change on the fly.

This would be similar to the galil eng. view's "custom command" option which has proven to be very useful in the past.

### Acceptance criteria
- [ ] A user can get an ADS variable through the beckhoff engineering view
- [ ] A user can set an ADS variable through the beckhoff engineering view

Inizia con la Beckhoff engineering view e l’integrazione di adsDriver, quindi verifica se l’asyn call può cambiare dinamicamente per una adhoc ADS variable. Confronta la custom command option della Galil engineering view come riferimento; il lavoro è completato quando gli utenti possono ottenere e impostare una ADS variable tramite la Beckhoff engineering view.

Scritto dal modello di indicizzazione a partire dal testo della issue.