Inconsistencies around customisation the `brainglobe_dir`

[alessandrofelder]

It is currently possible to

atlas = BrainGlobeAtlas("some_atlas", brainglobe_dir=Path("some_non_default_dir"))

and it will download and store the atlas data in a non-default directory but this will not be listed in the return values of get_downloaded_versions.

Not sure what the best way forward is. Maybe:

• pass brainglobe_dir as an optional argument to the functions, like get_downloaded_versions(brainglobe_dir=None) etc.