Add resample force kwarg

[ameraner]

This PR adds a force kwarg to the resampler.resample call. When set to True, it bypasses the area equality checks that skip the resampling if the geometries are the same. This is useful e.g. when data has NaN gaps (for example after a parallax correction) and one wants to gapfill it, e.g. with nearest neighbour.

• Closes Pyresample cannot be used for gapfilling due to geometries_are_the_same check #660
• Tests added
• Tests passed
• Fully documented

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.68%. Comparing base (3b1287b) to head (2e7a3c8).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #726      +/-   ##
==========================================
+ Coverage   93.66%   93.68%   +0.02%     
==========================================
  Files          89       89              
  Lines       13707    13715       +8     
==========================================
+ Hits        12838    12849      +11     
+ Misses        869      866       -3     

Flag	Coverage Δ
unittests	93.68% <100.00%> (+0.02%)	⬆️

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[djhoese]

Looks good to me. I can't help but think this smells like we're doing something wrong in Satpy's design that this is needed.

[djhoese]

I was pretty sure when I last reviewed this there was another location I found where this equality/comparison needs to be forced, but now I can't find it. It may have just been that we'll need to keep this in mind when I do further work on the pyresample.future resampler stuff.