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>

templates/gitea/deprecation.yaml

@@ -70,6 +70,11 @@
     {{- fail "`resources` does no longer exist. Please refer to the changelog and configure `deployment.gitea.resources` instead." -}}
   {{- end -}}
 
+  {{/* REPLICA COUNT */}}
+  {{- if .Values.replicaCount -}}
+    {{- fail "`replicaCount` does no longer exist. Please refer to the changelog and configure `deployment.replicas` instead." -}}
+  {{- end -}}
+
   {{/* SCHEDULER NAME */}}
   {{- if .Values.schedulerName -}}
     {{- fail "`schedulerName` does no longer exist. Please refer to the changelog and configure `deployment.schedulerName` instead." -}}