chore(helm): switch from Deployment to StatefulSet (#1901)

Jellyseerr is not designed to support multiple concurrently running instances.
To ensure that only one instance can run at any given time we:

- Replace Deployment with StatefulSet: switch from running "at least N pods" to
  "at most N pods".
- Remove replicaCount value: default is 1, we do not want to support more.

charts/jellyseerr-chart/templates/statefulset.yaml

@@ -1,13 +1,11 @@
 apiVersion: apps/v1
-kind: Deployment
+kind: StatefulSet
 metadata:
   name: {{ include "jellyseerr.fullname" . }}
   labels:
     {{- include "jellyseerr.labels" . | nindent 4 }}
 spec:
-  replicas: {{ .Values.replicaCount }}
-  strategy:
-    type: {{ .Values.strategy.type }}
+  serviceName: {{ include "jellyseerr.fullname" . }}
   selector:
     matchLabels:
       {{- include "jellyseerr.selectorLabels" . | nindent 6 }}