Add new (Eumetrain) FCI RGB composites

[ameraner]

This PR adds a series of RGB composites for FCI. In most cases, the new RGBs reuse existing recipes, and will have to be tuned further to account for the specific FCI properties (SRF, resolution, etc).

It adds the composites:

• night_ir105 for a simple nighttime layer to be used to fill the night-time part in day-only RGBs (see below). This was used for the EUMETSAT FCI first image and commissioning publications.
• night_ir_alpha, as well as the according night_ir_with_background and night_ir_with_background_hires, as known from e.g. SEVIRI
• true_color_with_night_ir105, true_color_with_night_ir, true_color_with_night_ir_hires, combining True Color with the night layers above
• cloud_type, cloud_phase and for each a day-night combination using night_ir105 (cloud_*_with_night_ir105)
• ir_sandwich , based on colorized_ir_clouds, as well as the day-night combination ir_sandwich_with_night_colorized_ir_clouds. Uses the same recipe as in SEVIRI, with the spectral colormap.
• fire_temperature, with the classic recipe, plus the variants _38refl with the reflective part of the 3.8µm channel and _rad with the channels in radiance units (here, the stretch limits have been computed by converting the radiance unit of the existing recipe limits)
• snow, since the according composite in visir.yaml is not being picked up due to the VIS0.8 channel starting only at 0.815, while the dependency looks for 0.8
• 24h_microphysics, which was missing completely in satpy, and is hence added to visir.yaml, using the standard EUM recipe from https://resources.eumetrain.org/RGBguide/recipes/RGB_recipes.pdf

By doing this, it contributes in several ways to https://github.com/pytroll/satpy/issues/2670. To close that issue, we still need to sort out a few midlatitude/tropical recipes: since this affects many shared recipes and is not specific to FCI, I would leave that to a different PR.

• [x] Contributes to #2670

After this PR, the list of available composites for FCI becomes:

24h_microphysics
airmass
ash
cimss_cloud_type
cimss_cloud_type_raw
cloud_phase
cloud_phase_distinction
cloud_phase_distinction_raw
cloud_phase_raw
cloud_phase_with_night_ir105
cloud_type
cloud_type_with_night_ir105
cloudtop
colorized_ir_clouds
convection
day_essl_colorized_low_level_moisture
day_essl_low_level_moisture
day_microphysics
dust
essl_colorized_low_level_moisture
essl_low_level_moisture
fire_temperature
fire_temperature_38refl
fire_temperature_rad
fog
geo_color
geo_color_background_with_low_clouds
geo_color_high_clouds
geo_color_low_clouds
geo_color_night
green_snow
ir108_3d
ir_cloud_day
ir_sandwich
ir_sandwich_with_night_colorized_ir_clouds
natural_color
natural_color_raw
ndvi_hybrid_green
ndvi_hybrid_green_fully_sunzencorrected
ndvi_hybrid_green_raw
night_fog
night_ir105
night_ir_alpha
night_ir_with_background
night_ir_with_background_hires
night_microphysics
rocket_plume_day
rocket_plume_night
snow
true_color
true_color_fully_sunzencorrected
true_color_raw
true_color_raw_with_corrected_green
true_color_reproduction
true_color_reproduction_corr
true_color_reproduction_uncorr
true_color_with_night_ir
true_color_with_night_ir105
true_color_with_night_ir_hires

A gallery of the new RGBs: cloud_phase cloud_phase_with_night_ir105 cloud_type cloud_type_with_night_ir105 true_color_with_night_ir105 true_color_with_night_ir ir_sandwich colorized_ir_clouds ir_sandwich_with_night_colorized_ir_clouds fire_temperature fire_temperature_38refl fire_temperature_rad snow 24h_microphysics

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[simonrp84]

Thanks for adding these! Just a note for now: The example image for the day/night blend with night lights background has the wrong name in the caption I think.

[coveralls]

Pull Request Test Coverage Report for Build 8691804714

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• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 0.0%

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[ameraner]

Thanks for adding these! Just a note for now: The example image for the day/night blend with night lights background has the wrong name in the caption I think.

Ah, indeed, thanks for noticing - our plotting tool uses the standard_name, which for composites does not always work well.. will need to fix :) (cc @strandgren ). I've added the correct composite name as text in the PR description.