Feature Request: Global environment variable configuration

[jalaziz]

The datadog helm chart installation has a top-level datadog.env configuration option which sets environment variables across all agents. It would be great if a similarly global option existed for the agent configuration CRD.

This can be particularly helpful for setting variables like DD_EC2_PREFER_IMDSV2.

Without it, the variable has to be set for each component which can redundant and error-prone.