Add CAMS cmorizer

[bettina-gier]

Description

Adding cmorizer for CAMS data

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• 🛠 Code is written according to the code quality guidelines
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New or updated data reformatting script

• 🛠 Documentation is available
• 🛠 The dataset has been added to the CMOR check recipe
• 🛠 The dataset has been added to the shared data pools of DKRZ and Jasmin by the @ESMValGroup/OBS-maintainers team
• 🧪 Numbers and units of the data look physically meaningful

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[lukruh]

Accepting the license at ads was not trivial for me, maybe we could drop a note with links to create account, setup cdsapirc file and accept licenses:

In doc/sphinx/source/input.rst change line 503 to:

.. [#note5] Downloading this dataset requires an ECMWF account with an [api key](https://cds.climate.copernicus.eu/how-to-api) in `~/.cdsapirc`. The corresponding licenses need to be accepted at [cds](https://cds.climate.copernicus.eu/profile?tab=licences)/[ads](https://ads.atmosphere.copernicus.eu/).

[lukruh]

Well done. The download once stopped due to rate limits (?) but after rerunning it everything worked fine. To be able to use --start and --end arguments some changes are required.
The resulting data looks fine. I found realistic values, patterns and sasonal cycles for nbp and fgco2. Units are correct and nothing suspicious found inspecting the meta data or fx files.

[lukruh]

Data looks good recipe_check_obs.yml completed. Downloader and formatter are working fine and I'm happy with the documentation. Good to go from my side. I can provide the path to the formatted data if some of the @ESMValGroup/obs-maintainers wants to have a look.