Add option to choose start time to MSI SAFE reader

[simonrp84]

Currently, the msi_safe reader uses the filename_info to get the start_time for a Scene. This can be problematic as multiple tiles can have the same start_time and will hence overwrite each other:

for files in [[tile1_files], [tile2_files]]:
   scn = Scene(files, reader='msi_safe')
   scn.load(['true_color'])
   scn.save_dataset('true_color')

The user would expect that two images are produced from this, one from each set of files. However, in many cases the second tile will overwrite the image saved by the first.

This PR attempts to fix the problem by allowing an optional reader_kwarg that allows the user to specify that the start_time should be read from the tile metadata rather than the filename:

for files in [[tile1_files], [tile2_files]]:
   scn = Scene(files, reader='msi_safe', reader_kwargs={'use_tile_time': True})
   scn.load(['true_color'])
   scn.save_dataset('true_color')

This will generate two output images as expected.

• Tests added
• Fully documented

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.57%. Comparing base (1742616) to head (3aea6ea).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2776      +/-   ##
==========================================
- Coverage   95.95%   94.57%   -1.38%     
==========================================
  Files         379      379              
  Lines       53861    53876      +15     
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- Hits        51680    50952     -728     
- Misses       2181     2924     +743     

Flag	Coverage Δ
behaviourtests	4.09% <0.00%> (-0.01%)	⬇️
unittests	95.16% <100.00%> (-0.89%)	⬇️

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[coveralls]

Pull Request Test Coverage Report for Build 9020466876

Details

• 18 of 18 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 96.032%

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Totals
Change from base Build 9020304102:	0.003%
Covered Lines:	51568
Relevant Lines:	53699

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💛 - Coveralls

[mraspaud]

LGTM, thanks for adding this functionality.

[mraspaud]

LGTM!