SANS Sample Changer: Delayed Move

As a: instrument Scientists on SANS2D

I would like the sample changer to have a delayed move. e.g. when I select the position to go to in the drop down of the OPI, it does not go there until I press set.

I would like my scripts to require no changes as part of adding this functionality.
I would like to still be able to manually type in the rack location in the selection box and press enter to move positions.
I would like to see where the rack will move too after selecting a rack position In the drop-down, but not move there until I press a separate button to move positions

### Acceptance Criteria
_What is the acceptance criteria?_
- [ ] Scripts do not require modification
- [ ] Users can still type rack locations into selection box in OPI and press enter key to move to a position
- [ ] Users can view where the sample rack will move to using the drop down before moving to the location
- [ ] Users can select a sample rack location using the drop down and then select a separate button to move to the position
- [ ] rack does no move when selecting the rack position in the drop down until the new button added is selected.

### Extra Information
_Why it is needed?_
- To make the OPI more like SECI.
- To make using the sample rack easier more intuitive for users

_Where required files/links are_
- Sample Changer: `EPICS\support\sampleChanger`
- Galil: `EPICS\support\galil\master\`
- Sample Changer OPI: `Instrument\Dev\ibex_gui\base\uk.ac.stfc.isis.ibex.opis\resources\stage` (Be aware that there is a Python script associated to the drop down menu and that the OPI has 2 prefixes for the Sans Sample Changer and Galil motors when working with the OPI)

## How to Test
_verbose instructions for reviewer to test changes
(**Add before making a PR**)_

Inizia leggendo i file del sample changer in EPICS/support/sampleChanger, i file Galil in EPICS/support/galil/master/ e le risorse OPI in Instrument/Dev/ibex_gui/base/uk.ac.stfc.isis.ibex.opis/resources/stage. Controlla lo script Python associato al dropdown e come vengono utilizzati i prefissi del sample changer SANS e del motore Galil. Il lavoro è completato quando il dropdown mostra un’anteprima senza eseguire movimenti, un pulsante separato esegue il movimento, le posizioni digitate e Enter continuano a funzionare e non sono necessarie modifiche agli script.

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