Helm: support adding backend environment variables from supercharts (#9214)

I have a need to add an environment variable for backend containers in
the Enterprise version. `additionalEnv` doesn't work very well for this,
because:

* It is an array, so if a user specifies a different value for it with
  `--set`, any defaults set by the superchart will disappear.

* It is inserted into the resource definition verbatim, so you can't
  refer to things like the release name.

This patch introduces a separate setting for this purpose. It takes a
map, and runs the variable values through `tpl` to support
interpolation.

Author: SpecLad

changelog.d/20250314_163649_roman_superchart_env.md

@@ -0,0 +1,5 @@
+### Added
+
+- \[Helm\] Added a new value, `cvat.backend.extensionEnv`, to support
+  supercharts adding environment variables to backend containers
+  (<https://github.com/cvat-ai/cvat/pull/9214>)

helm-chart/templates/_helpers.tpl

@@ -138,6 +138,11 @@ The name of the service account to use for backend pods
 - name: CVAT_NUCLIO_FUNCTION_NAMESPACE
   value: "{{ .Release.Namespace }}"
 {{- end }}
+
+{{- range $envName, $envValueTemplate := .Values.cvat.backend.extensionEnv }}
+- name: {{ $envName | toYaml }}
+  value: {{ tpl $envValueTemplate $ | toYaml }}
+{{- end }}
 {{- end }}
 
 {{- define "cvat.sharedClickhouseEnv" }}

helm-chart/values.yaml

@@ -15,6 +15,11 @@ cvat:
     affinity: {}
     tolerations: []
     additionalEnv: []
+
+    # This should only be used by supercharts;
+    # to set custom environment for a Helm release, use additionalEnv.
+    extensionEnv: {}
+
     additionalVolumes: []
     additionalVolumeMounts: []
     # -- The service account the backend pods will use to interact with the Kubernetes API