Add a `cmd` fragment support directory

As a developer I would like to be able to easily share IOCs with other facilities and try and keep related code together. To do this it was decided in https://github.com/ISISComputingGroup/IBEX/issues/6131 that we split the st.cmd file into the device specific part and the ISIS specific part, the device specific part (e.g. which dbs to load and baud rates) will move into the support directory.

## Acceptance Criteria
For one IOC:
* There is a cmd fragment in the support directory
* The IOC(s) in the ioc directory hold the ISIS specific stuff (e.g. config management) and call this cmd fragment
* There is a test IOC in the support directory that runs this fragment and can talk to the actual device