Create `fastcs-serial` repo for serial devices without manufacturer library dependencies

This is a record of a discussion with @gilesknap on how we would implement and containerise simple fastCS devices.

- a single repo shall be published that implements all fastCS serial devices
- the granularity of repositories would be that devices are grouped by dependency - hence simple serial devices go in a single repo
- thus a single container is published that includes support for all such devices
- in this scheme, a complex device that has vendor specific library dependencies would get its own individual repo and container.