feat(deployment)!: move replicaCount to deployment.replicas

The top-level `replicaCount` value only ever set the replica count of the Gitea Deployment, but was declared next
to chart-wide settings. Moving it into the `deployment` dict completes the consolidation already done for
`affinity`, `dnsConfig`, `nodeSelector`, `priorityClassName`, `resources`, `schedulerName`, `strategy`,
`tolerations` and `topologySpreadConstraints`.

The key was renamed from `replicaCount` to `replicas` at the same time. Every other key inside the `deployment`
dict mirrors the name of the corresponding Kubernetes field, so `deployment.replicas` maps one to one onto
`spec.replicas` and removes the need to remember a chart-specific alias.

A deprecation check fails the release when the removed top-level value is still set. Silently ignoring it would
be severe here: the release would scale back down to a single replica without any warning, and the HA guards in
the PVC and config templates, which key off the replica count, would no longer apply.

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

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

unittests/helm/deployment/deprecations.yaml

@@ -60,6 +60,12 @@ 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 `replicaCount` value is set
+    set:
+      replicaCount: 2
+    asserts:
+      - failedTemplate:
+          errorMessage: "`replicaCount` does no longer exist. Please refer to the changelog and configure `deployment.replicas` instead."
   - it: fails when the removed `schedulerName` value is set
     set:
       schedulerName: stork
@@ -104,6 +110,7 @@ tests:
       nodeSelector:
         foo: bar
       priorityClassName: high-priority
+      replicaCount: 2
       resources:
         limits:
           cpu: 100m