Add introspection of commands in odin data applications

[GDYendell]

Commands are now supported via odin-detector/odin-data#359, so fastcs-odin should introspect these and create Attributes.

I think we want new type of summary attribute that would allow us to create an AttrRW() that when set pokes other attributes to send the commands, and reads from an AttrR for its current state. In this case when set to 1 it would poke "start_writing", when set to 0 it would poke "stop_writing" and update its readback from "writing". This could possibly be a separate issue if it proves complicated and this one can just be for creating the PVs for individual commands.

• Depends on Update odin data adapter to expose commands odin-detector/odin-data#363