Implement guess-can-open for Backends

[kmuehlbauer]

• xradar version: latest
• Python version: all
• Operating System: all

Description

In #205 @syedhamidali is proposing a technique to read/open any (unknown) radar data file by trying the different backends sequentially. Over in xarray one can implement a guess_can_open function which checks a file if it can be opened by this backend.

I'm suggesting to implement this function for all our backends (if this is possible at all) and then revisit #205.