Add reader for CAMEL emissivity datasets.

[simonrp84]

This PR adds a reader for the NASA / USGS CAMEL emissivity product, which is a Level 3 global, gridded, dataset of IR emissivity values at 13 spectral tie points.

As well as the emissivity data, this reader also supports the ancillary datasets (ndvi, quality flags, etc).

• 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 96.13%. Comparing base (869e4fe) to head (0a5720e).
Report is 92 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3023    +/-   ##
========================================
  Coverage   96.13%   96.13%            
========================================
  Files         383      385     +2     
  Lines       55688    55802   +114     
========================================
+ Hits        53534    53648   +114     
  Misses       2154     2154            

Flag	Coverage Δ
behaviourtests	3.88% <0.00%> (-0.01%)	⬇️
unittests	96.23% <100.00%> (+<0.01%)	⬆️

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[coveralls]

Pull Request Test Coverage Report for Build 12648250966

Details

• 115 of 115 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.008%) to 96.2%

---

Totals
Change from base Build 12572361608:	0.008%
Covered Lines:	53363
Relevant Lines:	55471

---

💛 - Coveralls

[pnuu]

Some small comments inline.

[simonrp84]

Thanks @pnuu! I've committed some changes that should address your comments.

[mraspaud]

LGTM