refactor(serviceAccount)!: group the values into existingServiceAccount and new

The previous notation mixed two concerns in a single flat dict: `create`/`name` decided whether the chart manages the
ServiceAccount or only references an externally provided one, while the remaining keys only ever applied to a
chart-managed ServiceAccount. That made `name` ambiguous, because it either renamed the generated object or pointed to a
foreign one, and it forced the deployment to guard the reference with `or .Values.serviceAccount.create
.Values.serviceAccount.name`.

The values are now grouped the same way as `persistence`, which was restructured in dfe087c. `serviceAccount.enabled`
controls whether the pod uses a ServiceAccount at all, `serviceAccount.existingServiceAccount` references an externally
managed object and `serviceAccount.new` holds the properties of the object created by the chart. The templates follow
the established helper layout in `templates/gitea/_serviceAccounts.tpl`.

Two latent bugs are fixed along the way. The annotation helper was defined as `gitea.secret.admin.annotations`, so the
`gitea.serviceAccount.annotations` include in the template never resolved. And the duplicated name helper
`gitea.serviceAccountName` in `templates/_helpers.tpl` is removed in favour of `gitea.serviceAccount.name`.

BREAKING CHANGE:
- `serviceAccount.create` does no longer exist. Use `serviceAccount.enabled` instead. The default changed from `false`
  to `true`, so a ServiceAccount is now created unless it is explicitly disabled.
- `serviceAccount.name` does no longer exist. Use `serviceAccount.existingServiceAccount.enabled` together with
  `serviceAccount.existingServiceAccount.existingServiceAccountName` to reference an externally managed ServiceAccount.
- `serviceAccount.annotations`, `serviceAccount.labels`, `serviceAccount.automountServiceAccountToken` and
  `serviceAccount.imagePullSecrets` moved below `serviceAccount.new`.

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

templates/gitea/serviceAccount.yaml

@@ -1,20 +1,20 @@
-{{- if .Values.serviceAccount.create }}
+{{- if eq (include "gitea.serviceAccount.enabled" .) "true" }}
+---
 apiVersion: v1
 kind: ServiceAccount
 metadata:
-  name: {{ include "gitea.serviceAccountName" . }}
-  namespace: {{ .Values.namespace | default .Release.Namespace }}
-  labels:
-    {{- include "gitea.labels" . | nindent 4 }}
-    {{- with .Values.serviceAccount.labels }}
-    {{- . | toYaml | nindent 4 }}
-  {{- end }}
-  {{- with .Values.serviceAccount.annotations }}
+  {{- with (include "gitea.serviceAccount.annotations" .) }}
   annotations:
-    {{- . | toYaml | nindent 4 }}
+    {{- . | nindent 4 }}
   {{- end }}
-automountServiceAccountToken: {{ .Values.serviceAccount.automountServiceAccountToken }}
-{{- with .Values.serviceAccount.imagePullSecrets }}
+  {{- with (include "gitea.serviceAccount.labels" .) }}
+  labels:
+    {{- . | nindent 4 }}
+  {{- end }}
+  name: {{ include "gitea.serviceAccount.name" . }}
+  namespace: {{ .Values.namespace | default .Release.Namespace }}
+automountServiceAccountToken: {{ .Values.serviceAccount.new.automountServiceAccountToken }}
+{{- with .Values.serviceAccount.new.imagePullSecrets }}
 imagePullSecrets:
   {{- . | toYaml | nindent 2 }}
 {{- end }}