feat (fabric-x): Make the Fabric-X channel configurable

Fabric-X generation currently assumes the default channel. Research where the channel name appears in the generated Fabric-X files and update the generator so the value comes from the normal Fablo config.

The implementation should keep the default generated network working, but a user should also be able to change the channel name in `fablo-config.json` and still run the Fabric-X flow successfully.

Trace the Fabric-X generation flow and the channel references in its generated files, then compare them with the normal values in fablo-config.json. Verify that the default generated network still works and that changing the channel name in fablo-config.json allows the Fabric-X flow to run successfully.

Written by the indexing model from the issue text.