✨(helm) add a job allowing to run arbitrary management command

For a specific deployment we may need to run a specific management
command, like the one added previously updating all files content-type.
A template is added responsible to manage this case. The job will be
created only if the backend.job.command is set.

src/helm/impress/Chart.yaml

@@ -1,5 +1,5 @@
 apiVersion: v2
 type: application
 name: docs
-version: 2.0.1-beta.7
+version: 2.0.1-beta.8
 appVersion: latest