Add a helper method to generate GIF Snapshots

[rpaschoal]

These changes add a helper method to generate GIF snapshots. Here is an example output of the input_3sec.mp4 resource test file with default parameters:

[codecov-commenter]

Codecov Report

Patch coverage: 86.95% and project coverage change: +0.45 🎉

Comparison is base (dc88862) 74.22% compared to head (3dc2fff) 74.68%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #419      +/-   ##
==========================================
+ Coverage   74.22%   74.68%   +0.45%     
==========================================
  Files         111      112       +1     
  Lines        2778     2824      +46     
==========================================
+ Hits         2062     2109      +47     
+ Misses        716      715       -1     

Impacted Files	Coverage Δ
FFMpegCore/FFMpeg/FFMpeg.cs	67.17% <72.72%> (+0.32%)	⬆️
FFMpegCore/FFMpeg/Arguments/GifPaletteArgument.cs	100.00% <100.00%> (ø)
FFMpegCore/FFMpeg/Enums/FileExtension.cs	38.88% <100.00%> (+3.59%)	⬆️
FFMpegCore/FFMpeg/FFMpegArgumentOptions.cs	85.00% <100.00%> (+0.25%)	⬆️
FFMpegCore/FFMpeg/SnapshotArgumentBuilder.cs	80.39% <100.00%> (+26.33%)	⬆️

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[rosenbjerg]

Hi @rpaschoal,
This looks great, thanks for the contribution to this project!

[rpaschoal]

Thanks @rosenbjerg , happy to contribute 🙂

Do you have an idea of when these changes might be going live in a new version over Nuget?