Add LandSeaFalseColorCompositor

[TAlonglong]

Add a compositor using the window IR channel, a land sea mask and computing a color palette based on these to generate a false color image. Clouds are shades of gray to white from the brightness temperature(IR window channel), land is greenish and sea is blueish.

Here is an small example using the FCI ir_105

With a composites config section as this:

  _land_sea_mask:
    compositor: !!python/name:satpy.composites.StaticImageCompositor
    standard_name: land_sea_mask
    filename: /home/trygveas/testdata/static_images/test_20140111_120000.tif

  land_sea_false_color:
    compositor: !!python/name:satpy.composites.LandSeaFalseColorCompositor
    standard_name: null_enhancement
    prerequisites:
      - ir_105
      - _land_sea_mask

• [X] Closes #2721
• [ ] Tests added
• [ ] Fully documented
• [ ] Add your name to AUTHORS.md if not there already

[TAlonglong]

It is possible that this can be achieved by using the palettized enhancement together with a mask from the land sea mask.

I have not looked into this, so I'm not sure if this is possible.

[codecov[bot]]

Codecov Report

Attention: 91 lines in your changes are missing coverage. Please review.

Comparison is base (bca22b4) 95.40% compared to head (adb4505) 95.24%.

Files	Patch %	Lines
satpy/composites/__init__.py	4.21%	91 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2722 +/- ## ========================================== - Coverage 95.40% 95.24% -0.17% ========================================== Files 371 371 Lines 52825 52920 +95 ========================================== + Hits 50399 50403 +4 - Misses 2426 2517 +91 ``` | [Flag](https://app.codecov.io/gh/pytroll/satpy/pull/2722/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | Coverage Δ | | |---|---|---| | [behaviourtests](https://app.codecov.io/gh/pytroll/satpy/pull/2722/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `4.15% <4.21%> (+<0.01%)` | :arrow_up: | | [unittests](https://app.codecov.io/gh/pytroll/satpy/pull/2722/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `95.85% <4.21%> (-0.17%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll#carryforward-flags-in-the-pull-request-comment) to find out more.

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[mraspaud]

I've done something similar in the past, using only configuration and palettes, I can try to dig it out if you want...

[coveralls]

Pull Request Test Coverage Report for Build 7552334306

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 95.802%

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Totals
Change from base Build 7472442128:	-0.2%
Covered Lines:	50529
Relevant Lines:	52743

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