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

The top-level `topologySpreadConstraints` value only ever configured the pod spec of the Gitea Deployment, yet
it lived next to chart-wide settings. This made it hard to tell which values influence the Deployment and which
apply to the chart as a whole. Moving it into the `deployment` dict continues the consolidation already done for
`affinity`, `dnsConfig`, `nodeSelector`, `priorityClassName` and `resources`, so all pod scheduling settings are
now grouped in one predictable place.

A deprecation check fails the release when the removed top-level value is still set. Silently ignoring it would
be particularly harmful here: the constraints would be dropped without any warning and all replicas could end up
scheduled on a single node or zone, defeating the availability guarantees the user configured.

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

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

unittests/helm/deployment/basic.yaml

@@ -139,6 +139,31 @@ tests:
       - equal:
           path: spec.template.spec.priorityClassName
           value: high-priority
+  - it: topologySpreadConstraints are undefined
+    template: templates/gitea/deployment.yaml
+    asserts:
+      - notExists:
+          path: spec.template.spec.topologySpreadConstraints
+  - it: topologySpreadConstraints are defined
+    template: templates/gitea/deployment.yaml
+    set:
+      deployment.topologySpreadConstraints:
+        - topologyKey: kubernetes.io/hostname
+          whenUnsatisfiable: DoNotSchedule
+          maxSkew: 1
+          labelSelector:
+            matchLabels:
+              app.kubernetes.io/instance: gitea-unittests
+    asserts:
+      - equal:
+          path: spec.template.spec.topologySpreadConstraints
+          value:
+            - topologyKey: kubernetes.io/hostname
+              whenUnsatisfiable: DoNotSchedule
+              maxSkew: 1
+              labelSelector:
+                matchLabels:
+                  app.kubernetes.io/instance: gitea-unittests
 
   - it: "injects TMP_EXISTING_ENVS_FILE as environment variable to 'init-app-ini' init container"
     template: templates/gitea/deployment.yaml