Update FCI reader for new test data release and add patches for IDPF data

[ameraner]

This PR adds minor modifications to the FCI reader:

• the index map retrieval mechanism is updated to use the index variable, to account for format changes in the upcoming test data release. The reader still works also with older test data.

• two patches (wrong geolocation paramters and earth_sun_distance data) are added to make the reader work also for IDPF data (as released e.g. to SAFs) as discussed on Slack.

• a note is added to the FCI example and docstring to note that hdf5plugin can be used for automatic decompression (while we fix the issues in Use hdf5plugin for FCI decompression #2043

• Tests added

• Fully documented

[mraspaud]

LGTM, just one small note

[codecov]

Codecov Report

Merging #2086 (bef97cc) into main (7386c43) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2086      +/-   ##
==========================================
+ Coverage   93.85%   93.89%   +0.04%     
==========================================
  Files         283      283              
  Lines       42417    42537     +120     
==========================================
+ Hits        39811    39942     +131     
+ Misses       2606     2595      -11     

Flag	Coverage Δ
behaviourtests	4.71% <0.00%> (-0.01%)	⬇️
unittests	94.45% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/readers/fci_l1c_nc.py	98.02% <100.00%> (+0.09%)	⬆️
satpy/tests/reader_tests/test_fci_l1c_nc.py	100.00% <100.00%> (ø)
satpy/modifiers/_crefl.py	92.40% <0.00%> (-0.62%)	⬇️
satpy/tests/test_crefl_utils.py	100.00% <0.00%> (ø)
satpy/tests/modifier_tests/test_crefl.py	100.00% <0.00%> (+0.51%)	⬆️
satpy/tests/test_config.py	94.61% <0.00%> (+0.76%)	⬆️
satpy/tests/reader_tests/test_vii_base_nc.py	100.00% <0.00%> (+1.24%)	⬆️
satpy/tests/reader_tests/test_nwcsaf_msg.py	100.00% <0.00%> (+1.80%)	⬆️
satpy/tests/reader_tests/test_vii_l1b_nc.py	100.00% <0.00%> (+2.81%)	⬆️
satpy/modifiers/_crefl_utils.py	95.09% <0.00%> (+3.04%)	⬆️
... and 1 more

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[coveralls]

Coverage increased (+0.005%) to 94.398% when pulling bef97cc on ameraner:feature_update_fci_reader_for_datacube_td into 67b11b2 on pytroll:main.