CMIP6Plus support for ESGF download

[ghossh]

Description

This pull request adds initial support for the CMIP6Plus project in ESMValCore. CMIP6Plus is the WCRP project used for climate model data published on ESGF after the formal closure of CMIP6. This PR enables ESMValCore to recognise CMIP6Plus as a project and to search/download data from ESGF where supported.

Changes in this pull request:

• Add CMIP6Plus to the ESGF facet configuration
• Add CMIP6Plus to the example ESGF data source configuration

Further CMIP6Plus-related improvements may be added in follow-up commits on
this branch.

Documentation Link:
https://esmvaltool--3160.org.readthedocs.build/projects/ESMValCore/en/3160/reference/facets.html#cmip6plus

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.42%. Comparing base (af639cb) to head (c8cb606).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3160      +/-   ##
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+ Coverage   96.41%   96.42%   +0.01%     
==========================================
  Files         280      280              
  Lines       16268    16271       +3     
==========================================
+ Hits        15684    15690       +6     
+ Misses        584      581       -3     

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[bouweandela]

Great addition @ghossh! It would be nice to add a bit more before merging:

• Add a documentation page, probably a copy of or addition to https://docs.esmvaltool.org/projects/ESMValCore/en/latest/reference/facets.html#cmip6
• Enable CMOR checks, here is the example for CMIP6:

  ESMValCore/esmvalcore/config/configurations/defaults/cmor_tables.yml

  Lines 10 to 15 in 1acf602

  	CMIP6:
  	cmor_table:
  	type: esmvalcore.cmor.table.CMIP6Info
  	paths:
  	- cmip6/Tables
  	- cmip6-custom

  . Are there special tables for CMIP6Plus or do they just use the CMIP6 CMOR tables?
• Add an entry to the configuration file for intake-esgf, as we recommend that people switch over to that because it supports the new ESGF search interface. It can be a copy of

  ESMValCore/esmvalcore/config/configurations/data-intake-esgf.yml

  Lines 3 to 16 in 1acf602

  	CMIP6:
  	data:
  	intake-esgf:
  	type: esmvalcore.io.intake_esgf.IntakeESGFDataSource
  	facets:
  	activity: "activity_drs"
  	dataset: "source_id"
  	ensemble: "member_id"
  	exp: "experiment_id"
  	institute: "institution_id"
  	grid: "grid_label"
  	mip: "table_id"
  	project: "project"
  	short_name: "variable_id"

• Add an entry to the local data source so people have a good example of how to organize the directory structure according to the official DRS, can be a copy of

  ESMValCore/esmvalcore/config/configurations/data-local.yml

  Lines 11 to 17 in 1acf602

  	CMIP6:
  	data:
  	local:
  	type: esmvalcore.io.local.LocalDataSource
  	rootpath: ~/climate_data
  	dirname_template: "{project}/{activity}/{institute}/{dataset}/{exp}/{ensemble}/{mip}/{short_name}/{grid}/{version}"
  	filename_template: "{short_name}_{mip}_{dataset}_{exp}_{ensemble}_{grid}*.nc"

It is also good to be aware that derived variables may need additional work in some cases, just like for CMIP7: #2984

[bouweandela]

Based on the information at https://wcrp-cmip.org/cmip-phases/cmip6plus/, it looks like the CMIP6Plus CMOR tables live at https://github.com/PCMDI/mip-cmor-tables/tree/main/Tables and the CV file would need to be copied from https://github.com/WCRP-CMIP/CMIP6Plus_CVs/blob/main/CVs/CMIP6Plus_CV.json