Get aperture positions from GDA aperture names

[olliesilvester]

Fixes DiamondLightSource/hyperion#1336

See Hyperion PR at:

Not to be merged until associated GDA changes are done

Instructions to reviewer on how to test:

1. Confirm tests pass

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[dperl-dls]

Great, thanks, just one comment

[DominicOram]

One small comment, otherwise looks good, thanks!

[DominicOram]

Great, thank you!