helm: Move some securityContext fields to container's securityContext

The `privileged` and `readOnlyRootFilesystem` fields are not valid in
the pod's security context and can only be used in the container's
security context. Trying to apply the generated resource would cause the
error:

```
error validating data: [ValidationError(Deployment.spec.template.spec.securityContext): unknown field "privileged" in io.k8s.api.core.v1.PodSecurityContext, ValidationError(Deployment.spec.template.spec.securityContext): unknown field "readOnlyRootFilesystem" in io.k8s.api.core.v1.PodSecurityContext]; if you choose to ignore these errors, turn validation off with --validate=false
```

helm/draino/templates/deployment.yaml

@@ -48,6 +48,10 @@ spec:
               port: 10002
           resources:
             {{- toYaml .Values.resources | nindent 12 }}
+          {{- with .Values.containerSecurityContext }}
+          securityContext:
+            {{- toYaml . | nindent 12 }}
+          {{- end }}
       serviceAccountName: {{ if .Values.rbac.create }}{{ template "draino.fullname" . }}{{ else }}"{{ .Values.rbac.serviceAccountName }}"{{ end }}
       {{- with .Values.securityContext }}
       securityContext:

helm/draino/values.yaml

@@ -46,5 +46,7 @@ securityContext:
   runAsGroup: 101
   runAsNonRoot: true
   runAsUser: 100
+
+containerSecurityContext:
   privileged: false
   readOnlyRootFilesystem: true