🔧(helm) allow specific env var for the backend and celery deploy

We want the possibility to configure specific environment variables on
backend and celery deployment. Most of them are common but in the case
of the newly added settings DB_PSYCOPG_POOL_MIN_SIZE we want to
configure ot only on the backend deployment, not on the celery or with a
different value.

src/helm/env.d/dev/values.impress.yaml.gotmpl

@@ -74,6 +74,12 @@ backend:
     Y_PROVIDER_API_BASE_URL: http://impress-docs-y-provider:443/api/
     Y_PROVIDER_API_KEY: my-secret
     CACHES_KEY_PREFIX: "{{ now | unixEpoch }}"
+  django:
+    envVars:
+      WEB_CONCURRENCY: 1
+      DB_PSYCOPG_POOL_MIN_SIZE: 10
+
+
   migrate:
     command:
       - "/bin/sh"