Add Gateway API HTTPRoute support to the Wiki.js Helm chart

[somaz94]

This adds an optional Gateway API HTTPRoute template to the Wiki.js Helm
chart, as an alternative to the existing Ingress for clusters that route
with a Gateway controller. It is disabled by default (httpRoute.enabled:
false), so clusters without the Gateway API CRDs are unaffected.

Changes:

• New templates/httproute.yaml, gated on httpRoute.enabled, backed by the
  existing Service (service.port).
• httpRoute block in values.yaml (enabled, annotations, hostnames,
  parentRefs) with inline comments.
• README: parameter table rows plus an "HTTPRoute (Gateway API)" section.

Validation (helm v3.18.1):

• helm lint --strict: pass
• httpRoute.enabled=false (default): nothing rendered
• httpRoute.enabled=true with parentRefs and hostnames: valid HTTPRoute
• enabled with hostnames omitted: hostnames field correctly dropped
• full chart render: no regressions

[somaz94]

Gentle nudge on this one — it's been a few weeks. This adds opt-in Gateway API HTTPRoute support to the Helm chart (default off → existing installs are unchanged). Happy to adjust anything if it helps. Thanks for maintaining Wiki.js!