[FEATURE]: Automatic update of demo code on HF Spaces

[aittalam]

Currently, the HF repo with the Spaces demo is updated manually when the code is updated.

It would be useful if we automatically updated the code when a new branch is merged with main (in particular if demo-related code is changed).

For the specific GH workflow code, we can get inspiration from the other blueprint repos. As part of this task and for easier copying of data, we might also want to move demo-specific code (e.g. synthetic datasets) to /demo.