add image comparison behave tests

[KatrinPoepp]

Pytroll image comparison dev behave tests as PR. This method of code transfer was proposed by Martin Raspaud.
Documentation for the behave tests will be provided with the rest of the project code.

[gerritholl]

The branch for this PR includes 322 MiB in data (8 PNG files), added in commit 1367072. We should probably upload those files somewhere (zenodo?) and then include code to download them on-the-fly, as to not pollute the git repository with large binary files. This may need rewriting the commit history?

[pnuu]

Yes, I think getting completely rid of the images from the repo requires rewriting the git history on force-pushing.

[gerritholl]

If we remove the images in a dedicated commit, then squash the commits before merge, would that be enough to remove the images from the git history?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.05%. Comparing base (f3a2343) to head (a326b11).
Report is 339 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2912      +/-   ##
==========================================
+ Coverage   95.97%   96.05%   +0.07%     
==========================================
  Files         368      373       +5     
  Lines       53973    54406     +433     
==========================================
+ Hits        51801    52259     +458     
+ Misses       2172     2147      -25     

Flag	Coverage Δ
behaviourtests	3.99% <ø> (-0.04%)	⬇️
unittests	96.14% <ø> (+0.07%)	⬆️

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[coveralls]

Pull Request Test Coverage Report for Build 11075540122

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 8 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.01%) to 96.15%

---

Files with Coverage Reduction	New Missed Lines	%
satpy/tests/utils.py	2	93.16%
satpy/tests/reader_tests/gms/test_gms5_vissr_l1b.py	3	98.67%
satpy/tests/reader_tests/gms/test_gms5_vissr_navigation.py	3	97.18%

Totals
Change from base Build 10957325874:	-0.01%
Covered Lines:	52493
Relevant Lines:	54595

---

💛 - Coveralls

[gerritholl]

Related to https://github.com/pytroll/image-comparison-tests-dev/pull/2