Description of problem:

The Backstage CRD allows to declare environment variables for the pod of RHDH and they are only added into the backstage-backend container, but not into the init container. There is an example of usage to declare the registry authentication file (`REGISTRY_AUTH_FILE`) to pull images successfully from a private container image registry.

Prerequisites (if any, like setup, operators/versions):

Tested in a RDHD instance operated by the Operator (but it seems that it could happen into an instance managed by the Helm Chart.)

Steps to Reproduce

1. Declare some environment variables in a Backstage CR as:

spec:
  application:
    appConfig:
      configMaps:
        - name: rhdh-app-config
      mountPath: /opt/app-root/src
    dynamicPluginsConfigMapName: rhdh-dynamic-plugins
    extraEnvs:
      envs:
        - name: NODE_TLS_REJECT_UNAUTHORIZED
          value: '0'
        - name: LOG_LEVEL
          value: debug
        - name: REGISTRY_AUTH_FILE
          value: /opt/app-root/src/.config/.dockerconfigjson 

1. Apply the changes and confirm the variables defined
2. The backstage-backend container includes them:
   
3. The install-dynamic-plugins init container does not include them:
   

Actual results:

The environment variables are only declared into the backend container.

Expected results:

The environment variables are also declared into the init container.

Reproducibility (Always/Intermittent/Only Once):

Build Details:

Additional info (Such as Logs, Screenshots, etc):

Another alternative it could be to define which environment variables must be declared for the init container. Maybe with an definition such as:

spec:
  application:
    appConfig:
      configMaps:
        - name: rhdh-app-config
      mountPath: /opt/app-root/src
    dynamicPluginsConfigMapName: rhdh-dynamic-plugins
    extraEnvs:
      envs:
        - name: NODE_TLS_REJECT_UNAUTHORIZED
          value: '0'
        - name: LOG_LEVEL
          value: debug
    initExtraEnvs:
      - name: REGISTRY_AUTH_FILE
        value: /opt/app-root/src/.config/.dockerconfigjson