Add a reader for Radarsat 2 SGF data

[mraspaud]

This PR adds a reader for Radarsat 2 SGF data.

• [ ] Add support for geolocation
• [ ] Add extra dependencies in setup.py
• [ ] Add new line in the documentation's reader table
• [x] Links to relevant format descriptions
• [x] Tests added
• [ ] Fully documented

Example output using the sar-ice-log composite

[codecov[bot]]

Codecov Report

Merging #1981 (d97d34d) into main (09e51f9) will decrease coverage by 0.00%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1981      +/-   ##
==========================================
- Coverage   93.53%   93.53%   -0.01%     
==========================================
  Files         279      281       +2     
  Lines       41325    41453     +128     
==========================================
+ Hits        38655    38774     +119     
- Misses       2670     2679       +9     

Flag	Coverage Δ
behaviourtests	4.76% <0.00%> (-0.02%)	:arrow_down:
unittests	94.07% <100.00%> (-0.01%)	:arrow_down:

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

Impacted Files	Coverage Δ
satpy/readers/sar_c_safe.py	97.22% <100.00%> (-0.01%)	:arrow_down:
satpy/readers/sar_rs02.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_radarsat02.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_vii_l2_nc.py	93.93% <0.00%> (-6.07%)	:arrow_down:
satpy/tests/reader_tests/test_vii_l1b_nc.py	97.18% <0.00%> (-2.82%)	:arrow_down:
satpy/tests/reader_tests/test_nwcsaf_msg.py	96.63% <0.00%> (-1.69%)	:arrow_down:
satpy/tests/reader_tests/test_vii_base_nc.py	98.75% <0.00%> (-1.25%)	:arrow_down:
satpy/tests/test_config.py	93.84% <0.00%> (-0.77%)	:arrow_down:

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