Hyperion should store snapshot images in the `jpegs` folder instead of data collection folder

Currently hyperion stores the snapshot images in the same directory as the data collection which means that when the data collection data is aged out, synchweb snapshots appear blank because the data has been removed.

Instead we should store in a parallel directory structure inside the top-level jpegs subfolder which will mean that the snapshots get preserved.

The directory is of the form:

`/dls/i03/data/2026/mx41060-14/jpegs`

whilst this could be something that agamemnon tells us it may be more practical for us to construct ourselves.

## Acceptance Criteria
- synchweb displays snapshots and they don't get deleted.