0.21.0 [monochart] Add `envFromFieldRefFieldPath` config

what

• [monochart] Add envFromFieldRefFieldPath config

why

• To be able to declare ENV vars from pod fields
• Example usage is Datadog APM to declare dynamic ENV var DD_AGENT_HOST from pod field status.hostIP

references

• https://docs.datadoghq.com/agent/kubernetes/apm/?tab=helm
• https://kubernetes.io/docs/tasks/inject-data-application/environment-variable-expose-pod-information/#use-pod-fields-as-values-for-environment-variables