Demo running a recipe using intake-esm and pangeo CMIP6 data stored on Google cloud

[bouweandela]

For demo purposes only, do not merge.

To try the demo, run:

# Activate the conda environment
pixi shell -e esmvalcore-dev
# Set up an empty configuration
export ESMVALTOOL_CONFIG_DIR=$HOME/esmvaltool_config_for_testing_intake_esm
mkdir $ESMVALTOOL_CONFIG_DIR
# Copy the Google cloud data source configuration file
esmvaltool config copy data-intake-esm-gcs.yml
# Run the example recipe
esmvaltool run --max-parallel-tasks=1 examples/recipe_python.yml

Note that this demo uses a slightly modified version of the code in ESMValGroup/ESMValCore#2690. Differences ESMValGroup/ESMValCore@intake-esm...intake-esm-demo