Allow more flexility in MISP-object template

[gallypette]

I see in app.py that you call PyMISP's update_objects.py script to update objects. This one goes on to fetch data from static_repo = "https://github.com/MISP/misp-objects/archive/main.zip" and it makes me sad.

Would it be possible to have a local git repo instead, and just call git pull on this repo for updates?

This way people can change the remote and calling app.py -py won't erase their custom objects.