refactor(ingress)!: skip the Ingress when the HTTP Service is disabled

An Ingress that points at a Service which the chart does not render is broken by definition: the backend reference
cannot resolve and the ingress controller reports the rule as unavailable. The render condition therefore now also
requires `service.http.enabled` and lives in the new `gitea.ingress.enabled` helper, so the same rule can be reused
by other templates instead of being duplicated.

The namespace is taken from `.Release.Namespace` again. The `namespace` value is not a documented chart parameter,
and letting a single resource opt out of the release namespace breaks `helm uninstall` and Argo CD pruning, because
neither tracks objects outside the release namespace.

The `ingress.className` default changes from an empty string to `nginx`. An empty class makes the cluster fall back
to the default IngressClass, which silently produces a different result per cluster; naming the controller the chart
is tested against makes the rendered output predictable.

The scattered ingress suites are consolidated into a single `unittests/helm/ingress/ingress.yaml` that pins the
release name, namespace and appVersion, as required by the testing conventions, and covers the enable/disable matrix,
annotations, labels, TLS and a custom HTTP port.

BREAKING CHANGE: The Ingress is no longer rendered when `service.http.enabled` is `false`. `ingress.className` now
defaults to `nginx` instead of the cluster's default IngressClass. The undocumented `namespace` value no longer
applies to the Ingress.

Co-authored-by: Copilot <copilot@github.com>

templates/gitea/_ingresses.tpl

@@ -8,6 +8,14 @@
 {{- end }}
 {{- end }}
 
+{{- define "gitea.ingress.enabled" -}}
+{{- if and .Values.ingress.enabled .Values.service.http.enabled -}}
+true
+{{- else -}}
+false
+{{- end }}
+{{- end }}
+
 {{/* labels */}}
 
 {{- define "gitea.ingress.labels" -}}