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/deprecations.yaml

@@ -60,6 +60,13 @@ tests:
     asserts:
       - failedTemplate:
           errorMessage: "`resources` does no longer exist. Please refer to the changelog and configure `deployment.gitea.resources` instead."
+  - it: fails when the removed `topologySpreadConstraints` value is set
+    set:
+      topologySpreadConstraints:
+        - topologyKey: kubernetes.io/hostname
+    asserts:
+      - failedTemplate:
+          errorMessage: "`topologySpreadConstraints` does no longer exist. Please refer to the changelog and configure `deployment.topologySpreadConstraints` instead."
   - it: skips the deprecation checks when `checkDeprecation` is disabled
     set:
       checkDeprecation: false
@@ -77,6 +84,8 @@ tests:
       resources:
         limits:
           cpu: 100m
+      topologySpreadConstraints:
+        - topologyKey: kubernetes.io/hostname
     asserts:
       - hasDocuments:
           count: 0