Modify 'git-obs file maintainership migrate' to filter out empty entries, ident by 2 and sort entries

[dmach]

No description provided.

[hramrach]

I don't really understand the need for those parameters.

In what protocol is a null value required?

In what case are unsorted keys required?

Adding those options makes the code more complex, and I don't see when those options would be needed.

[hramrach]

Also #2118 now passes tests while this still does break some.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 33.94%. Comparing base (fb9ba30) to head (5c240dc).
⚠️ Report is 19 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2126      +/-   ##
==========================================
+ Coverage   33.90%   33.94%   +0.03%     
==========================================
  Files         196      199       +3     
  Lines       26988    27035      +47     
==========================================
+ Hits         9151     9177      +26     
- Misses      17837    17858      +21     

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[ncounter]

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