Outline chart: security hardening, configurable probes, flexible ingress

- Pod and container securityContext are now values-configurable
  (outline.securityContext.pod/container) with hardened defaults:
  runAsNonRoot (uid/gid 1001, the upstream image's nodejs user),
  readOnlyRootFilesystem, allowPrivilegeEscalation false, all
  capabilities dropped. /tmp is mounted as an emptyDir for Outline's
  import/export scratch files.
- Probes moved to values (outline.livenessProbe/readinessProbe/
  startupProbe); defaults are exactly the previously hardcoded ones.
- Ingress raised to the repo standard: ingress.className (default
  nginx), ingress.annotations merged with the always-set annotations,
  ingress.enabled flag; domain/clusterIssuer stay required and the
  TLS secret name was already conform.
- Additive outline.env block rendered through tpl with value/
  secretKeyRef/configMapKeyRef forms; chart-managed env stays in the
  template.

Major bump 3.1.1+up1.9.2 -> 4.0.0+up1.9.2 (runtime behavior changes
through hardening).

Part of #32

outline/Chart.yaml

@@ -5,7 +5,7 @@ icon: https://raw.githubusercontent.com/outline/outline/main/public/images/icon-
 
 type: application
 
-version: 3.1.1+up1.9.2
+version: 4.0.0+up1.9.2
 appVersion: 1.9.2
 
 maintainers: