IMAT: Make homing lens adjustment easier

As an IS on IMAT I would like to be able to home the lens adjustment axis without having to manually run a script to turn off the encoder.

The lens adjustment axis can interfere with data collection and so we turn off the encoder via a relay when we finish every general move (https://github.com/ISISComputingGroup/IBEX/issues/4379). A general move will then turn it on before starting but his is not done on a home and so the scientist must turn it on with a script before they home.

## Acceptance Criteria
* Investigate a hardware solution that means the encoder doesn't need to be turned off (e.g. a bit of tape)
* If a hardware solution is not possible then make sure the encoder is turned on when homing