Enable NWCSAF-GEO composites for ABI, AHI, FCI

[gerritholl]

Currently the NWCSAF-GEO composites only for for SEVIRI. This PR
enables them for the other geostationary imagers supported by NWCSAF-GEO
as well: ABI, AHI, and FCI.

• Closes Make nwcsaf-geo composites available to other geostationary imagers besides SEVIRI #1134
• Tests added
• Tests passed
• Passes flake8 satpy
• Fully documented

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[gerritholl]

Currently this PR copy-pastes the YAML code from the seviri.yaml file to each of abi.yaml, ahi.yabl, and fci.yaml. This is a hard to maintain solution that violates Don't Repeat Yourself (DRY). I don't know how I can avoid that, seeing that YAML apparently does not support includes and that visir.yaml already contains composites with the same names but expecting nwcsaf-pps data. Pending a solution to that I've put this PR in draft mode. It works, it passes tests, but it's not a good solution yet.

[coveralls]

Coverage decreased (-0.003%) to 89.605% when pulling 68e99a4 on gerritholl:enable-nwcsaf-other-geo into 446af3a on pytroll:master.

[codecov]

Codecov Report

Merging #1136 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1136      +/-   ##
==========================================
- Coverage   89.60%   89.60%   -0.01%     
==========================================
  Files         200      200              
  Lines       29484    29484              
==========================================
- Hits        26420    26419       -1     
- Misses       3064     3065       +1     

Impacted Files	Coverage Δ
satpy/scene.py	90.01% <0.00%> (-0.18%)	⬇️

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[gerritholl]

@pytroll/core This PR currently duplicates YAML code between seviri.yaml, abi.yaml, ahi.yaml, and fci.yaml (I dislike that, therefore it's still a draft). How can I adapt it to avoid this duplication, considering that visir.yaml is already occupied by nwcsaf-pps-based composites of the same name (but with differently named prerequisites)?

[djhoese]

From what I see we have four choices:

1. What you're doing now.
2. Move them to visir.yaml
3. Refactor the composite loading to load all/most YAMLs (similar to what's been discussed in the various plugin issues/PRs). We could then make a YAML for nwcsaf-specific composites.
4. Create a separate package that includes these configs similar to fogpy.

[gerritholl]

start behave test

[rymdulf]

Starting to clone and test the repository pytroll/satpy

[rymdulf]

The testing process was executed successfully. See the test results for this pull request here!