Add missing CfRadial1 features

[kmuehlbauer]

The Cfradial1 reader is still missing some bits and pieces. For that it would be great to have some example files:

• dual frequency cases would be great to have
• sweep subgroup cases would be interesting (also for testing)
• any other case where the current reader lacks

[syedhamidali]

I recently created the issue https://github.com/openradar/xradar/issues/134, and I think it is relevant to this issue as well.