Add support for EO-SIP AVHRR LAC data

[mraspaud]

This PR fixes a couple of things in the avhrr gaclac reader to accept EO-SIP (ESA) format LAC data

• Closes #xxxx
• Tests added
• Fully documented
• Add your name to AUTHORS.md if not there already

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.92%. Comparing base (45f918e) to head (5ffe15e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2762   +/-   ##
=======================================
  Coverage   95.92%   95.92%           
=======================================
  Files         377      377           
  Lines       53468    53489   +21     
=======================================
+ Hits        51287    51310   +23     
+ Misses       2181     2179    -2     

Flag	Coverage Δ
behaviourtests	4.10% <0.00%> (-0.01%)	⬇️
unittests	96.02% <100.00%> (+<0.01%)	⬆️

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[coveralls]

Pull Request Test Coverage Report for Build 8348304532

Details

• 25 of 25 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.006%) to 96.005%

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Totals
Change from base Build 8282476634:	0.006%
Covered Lines:	51182
Relevant Lines:	53312

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💛 - Coveralls

[sfinkens]

👍 The logic for finding the reader class, sensor etc could be moved to a separate method, otherwise looks good to me!

[sfinkens]

LGTM!