Fix area definition YAML not warning on typos

[djhoese]

If a user has a typo or some other unused parameter in an area YAML definition then pyresample silently ignores it and the user is left confused as to why things aren't working as expected. This PR fixes this by producing a UserWarning in these cases.

I could make this an error but I feel that limits the future flexibility and maintainability of the YAML reading. I could also make a configuration (pyresample.config) parameter that controls whether this is a warnings or error...or maybe just another keyword argument, but I'm not sure we need any more kwargs for these functions.

TODO: I'd like to rework some of the metadata handling in the future area definitions. I might not do that in this PR as it is decently separate. I noticed while working on this that any unused kwarg is put into the future AreaDefinition's .attrs dictionary property. This is error prone as it means that any unrecognized property will go in as "metadata". I'd like to add an explicit attrs: section to the YAML for defining these metadata values.

• Closes errors in area definition should not be silently ignored #570
• Tests added
• Tests passed
• Passes git diff origin/main **/*py | flake8 --diff
• Fully documented

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (eaf8367) 94.05% compared to head (26d8dc9) 94.06%.

Files	Patch %	Lines
pyresample/area_config.py	92.85%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #577   +/-   ##
=======================================
  Coverage   94.05%   94.06%           
=======================================
  Files          90       90           
  Lines       13575    13590   +15     
=======================================
+ Hits        12768    12783   +15     
  Misses        807      807           

Flag	Coverage Δ
unittests	94.06% <95.00%> (+<0.01%)	⬆️

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[coveralls]

coverage: 93.656% (+0.007%) from 93.649%
when pulling 26d8dc9 on djhoese:warn-unused-area-params
into eaf8367 on pytroll:main.

[mraspaud]

LGTM, thanks!