feat(deployment)!: move dnsConfig to deployment.dnsConfig

`dnsConfig` was a top-level value although it exclusively configures the pod spec of the Gitea Deployment. With
`affinity` and `env` already moved into the `deployment` dict, keeping `dnsConfig` at the root level leaves the
Deployment configuration split across two places and makes it harder to see which values end up in the rendered
pod spec.

Moving it into the `deployment` dict continues the consolidation of Deployment-scoped values and keeps the
values structure predictable for the remaining pod-level settings.

A deprecation check is added so that existing installations fail fast with an actionable error message. Without
it, a custom DNS configuration would be dropped silently, which typically surfaces much later as unexplained
name resolution failures inside the Gitea pod.

BREAKING CHANGE: `dnsConfig` no longer exists. Use `deployment.dnsConfig` instead. Installations that still set
`dnsConfig` will fail unless `checkDeprecation` is set to `false`.

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

unittests/helm/deployment/basic.yaml

@@ -103,6 +103,29 @@ tests:
                         operator: In
                         values:
                           - linux
+  - it: dnsConfig is undefined
+    template: templates/gitea/deployment.yaml
+    asserts:
+      - notExists:
+          path: spec.template.spec.dnsConfig
+  - it: dnsConfig is defined
+    template: templates/gitea/deployment.yaml
+    set:
+      deployment.dnsConfig:
+        nameservers:
+          - 192.0.2.1
+        options:
+          - name: ndots
+            value: "2"
+    asserts:
+      - equal:
+          path: spec.template.spec.dnsConfig
+          value:
+            nameservers:
+              - 192.0.2.1
+            options:
+              - name: ndots
+                value: "2"
 
   - it: "injects TMP_EXISTING_ENVS_FILE as environment variable to 'init-app-ini' init container"
     template: templates/gitea/deployment.yaml