feat: support CLOUDSDK_CONFIG env var

[gullitmiranda]

Add support to use the env CLOUDSDK_CONFIG to find .default-cloud-sdk-components file to have the same behaviour as gcloud SDK.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Usage examples

export CLOUDSDK_CONFIG="$HOME/.config/gcloud"
echo 'kubectl' >> $CLOUDSDK_CONFIG/.default-cloud-sdk-components
asdf plugin add gcloud
asdf install gcloud latest

Checklist:

• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[jthegedus]

Thanks