* Extend operator configuration to allow for a pod_environment_secret just like pod_environment_configmap
* Add all keys from PodEnvironmentSecrets as ENV vars (using SecretKeyRef to protect the value)
* Apply envVars from pod_environment_configmap and pod_environment_secrets before doing the global settings from the operator config. This allows them to be overriden by the user (via configmap / secret)
* Add ability use a Secret for custom pod envVars (via pod_environment_secret) to admin documentation
* Add pod_environment_secret to Helm chart values.yaml
* Add unit tests for PodEnvironmentConfigMap and PodEnvironmentSecret - highly inspired by @kupson and his very similar PR #481
* Added new parameter pod_environment_secret to operatorconfig CRD and configmap examples
* Add pod_environment_secret to the operationconfiguration CRD
Co-authored-by: Christian Rohmann <christian.rohmann@inovex.de>