🔒(helm) set default security context

In order to be able to deploy this in a restricted k8s cluster, we set
this default security context.

We set it as default because it doesn't change the way the app runs.

So it is better to be more secured by default.

Signed-off-by: Pierre Ozoux Krebber <pierre@ozoux.net>

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to
 - ✨(backend) add documents/all endpoint with descendants #1553
 - ✅(export) add PDF regression tests #1762
 - 📝(docs) Add language configuration documentation #1757
+- 🔒(helm) Set default security context #1750
 
 ### Fixed