Clean up ApertureValue to be nicer strings

[DominicOram]

Following #267 we have decoupled the enum used to set the aperture/scatterguard from that used in the GDA parameter files. However, the values of ApertureValue are still coupled to GDA as they are the strings that GDA will send to Hyperion when selecting the aperture. Thus we still have them set to SMALL_APERTURE etc. It would be cleaner to change them to more human readable values like Small as they are also what ends up in ispyb, this would mean we could remove the logic of changing the str interpretation

Note

It may just be easier to just do this once we no longer have GDA calling Hyperion

Acceptance Criteria

• ApertureValues enum is more human readable