support Radiant Earth MLHub

[cholmes]

I get an http error when trying to add https://api.radiant.earth/mlhub/v1/

Would be great to make sure that works.

[koyo-jakanees]

@cholmes I can start checking the issues as per the draft and order. Thanks(Davince)

[volaya]

Same problem as #85

Once the URL is correctly entered without the trailing slash, the connection works fine and the list of collections is shown. However, searching does not work, since the server seems to require auth and returns a 401 Unauthorized response