Create plan to optimise transmission using OAV images

Plan should do something like this:
- Move beamline into position for scintillator (+ move scint in)
- Take image of OAV
- Open image and get max pixel intensity
- If max is above target value, then lower transmission, if higher than raise transmission
- Do this with a binary search - i.e if saturation is too high then move transmission to (current trans + lowest trans / 2)
- Repeat this until we're sufficiently close to the target saturation value (~50%?)

## Acceptance Criteria
- Specific criteria that will be used to judge if the issue is fixed