feat: update DatadogAgent CRD v2alpha1 to v1.21.0

- Extracted from datadog-operator v1.21.0 release (December 17, 2025)
- Includes CSI driver configuration under spec.global.csi
- Adds 1,740 field descriptions that were missing in the original schema
- Generated using openapi2jsonschema.py utility as per repository guidelines

Key improvements:
- CSI driver support for Unix Domain Socket volumes
- Complete field descriptions for better developer experience
- Updated schema validations
- Additional security and performance features

Source: https://github.com/DataDog/datadog-operator/releases/tag/v1.21.0
CRD: https://raw.githubusercontent.com/DataDog/datadog-operator/v1.21.0/config/crd/bases/v1/datadoghq.com_datadogagents.yaml

Author: ryanfarisco