GUI OPIs: Move the OPIs into their own repo, mirrored into the GUI

As someone developing OPIs for use in the IBEX client, I want to be able to get the OPIs from the server (see https://github.com/ISISComputingGroup/IBEX/issues/6562 for the discussion), moving the OPIs into their own repo will aid this endeavour

## Acceptance Criteria
- [ ] There is a repo added to the EPICS server structure (at time of writing this would be a submodule), referred to here and in other related tickets, as "server OPI repo" - this is not necessarily a good name for the production system
- [ ] The githook(s) which ensure that the OPIs are functional (e.g. adding the dummy button) are moved to the server OPI repo
- [ ] There is an automated step which updates the appropriate folder in the GUI repo with the information from the server OPI repo that is triggered from the server side
- [ ] That automated step is added to the appropriate build pipelines
- [ ] The developer wiki is updated to cover the new workflow of `create OPI in server OPI repo` rather than the existing workflow