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/HA.yaml

@@ -14,7 +14,8 @@ tests:
   - it: fails with multiple replicas and "GIT_GC_REPOS" enabled
     template: templates/gitea/secret_config.yaml
     set:
-      replicaCount: 2
+      deployment:
+        replicas: 2
       persistence:
         accessModes:
           - ReadWriteMany
@@ -29,14 +30,16 @@ tests:
   - it: fails with multiple replicas and RWX file system not set
     template: templates/gitea/secret_config.yaml
     set:
-      replicaCount: 2
+      deployment:
+        replicas: 2
     asserts:
       - failedTemplate:
           errorMessage: "When using multiple replicas, a RWX file system is required and persistence.accessModes[0] must be set to ReadWriteMany."
   - it: fails with multiple replicas and bleve issue indexer
     template: templates/gitea/secret_config.yaml
     set:
-      replicaCount: 2
+      deployment:
+        replicas: 2
       persistence:
         accessModes:
           - ReadWriteMany
@@ -50,7 +53,8 @@ tests:
   - it: fails with multiple replicas and bleve repo indexer
     template: templates/gitea/secret_config.yaml
     set:
-      replicaCount: 2
+      deployment:
+        replicas: 2
       persistence:
         accessModes:
           - ReadWriteMany