i15-1: Implement shapshot cameras

I15-1 take snapshot images of the beamline before and after each scan, and submit these to ispyb. Currently the snapshot mechanism supports `cam1`, `cam2`, `web1` and `web2`, though currently, not all cameras are used.

The cameras have PV prefixes of

- `BL15J-DI-CAM-01`
- `BL15J-DI-CAM-02`
- `BL15J-DI-WEB-01`
- `BL15J-DI-WEB-02`

A brief description of the issue, including specific stakeholders and the business case where appropriate

These cameras and their snapshot functionality need to be implemented in Bluesky.
## Acceptance Criteria
- Be able to run a plan from GDA to collect some or all of these images as a 'before' or 'after' snapshot.