Blueapi doesn't specify plans need to be added to __init__.py for plans to be correctly registered

[oliwenmandiamond]

When adding new plans in my plans repository, I could get the BlueAPI PVC to pick up the changes but blueapi itself would still not have visibility of the new plans. After many hours trying to debug this, we eventually found that it was because the plans were not included in the __init__.py file with __all__ = [<plan_name>, ...].

It should be documented clearly that in order for BlueAPI to register plans from repositories, they must be added to the __init__.py.