Correction for output mediator passed to WriteHeader #5184

[kev365]

Fixes #5184.

ExportEvents passed the plaso.output.mediator module to WriteHeader instead of
the OutputMediator it had just created, so psort.py -o kml failed with
AttributeError: module 'plaso.output.mediator' has no attribute 'encoding'.

Also adds the end-to-end test for the kml output format, modelled on
output_rawpy.

A note on the reference output: KMLOutputModule.WriteFieldValues returns early for
events without latitude and longitude, and test_data/psort_test.plaso has no
geolocation data, so test_data/end_to_end/kml.log is the header and footer only:

<?xml version="1.0" encoding="utf-8"?><kml xmlns="http://www.opengis.net/kml/2.2"><Document></Document></kml>

That covers the defect, since it is in WriteHeader. It does not cover the placemark
path in WriteFieldValues, and there is currently no clean way to: android_airtag
appears to be the only parser that populates latitude and longitude, and the
AirGuard beacon table it reads stores latitude in the column named longitude and
longitude in the column named latitude
(reference). The plugin
does not compensate for that, so a placemark reference generated from
test_data/android/attd_db would record reversed coordinates. Noted for the record,
not addressed here.

Verified with the full end-to-end suite on Ubuntu 26.04, exit 0, including the new
output_kml case.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.10%. Comparing base (c69255f) to head (9fcec2a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5186   +/-   ##
=======================================
  Coverage   85.10%   85.10%           
=======================================
  Files         456      456           
  Lines       41089    41089           
=======================================
  Hits        34967    34967           
  Misses       6122     6122           

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[joachimmetz]

LGTM

[joachimmetz]

Thanks for the proposed changes