Reflectometry: Define behaviour of activating Disabled Mode during an active move

We should define what we expected the behaviour to be in the event a user activates Disabled Mode during a current move (e.g., In NR Mode perform a move all instruction and then set Disabled Move).

Disabled Mode allows the uses to move components on the beam line relative to a snapshot of the beam at the moment it was switched. If a move has not been completed I would be sceptical that a user would have desired to have this snap-shot at a pre-move completed moment in time.

I'm inclined to say that we should disable the ability to enter disabled mode until the beam line is stationary for pragmatic reasons. We should directly ask instrument scientists what their expected behaviour would be though.

## Acceptance Criteria
- [ ] We have documentation for instrument scientists expected behaviour
- [ ] A ticket is created to implement the defined behaviour