fix nextcloud db-username + k8s-dashboard chart repo

- nextcloud: add db-username to ESO secret template and usernameKey
  to chart values (required by newer chart version)
- k8s-dashboard: update chart repo URL to kubernetes-retired.github.io
  (old kubernetes.github.io/dashboard returns 404)

stacks/k8s-dashboard/main.tf

@@ -47,7 +47,7 @@ resource "helm_release" "kubernetes-dashboard" {
   namespace = kubernetes_namespace.k8s-dashboard.metadata[0].name
   name      = "kubernetes-dashboard"
 
-  repository = "https://kubernetes.github.io/dashboard/"
+  repository = "https://kubernetes-retired.github.io/dashboard/"
   chart      = "kubernetes-dashboard"
   atomic     = true
   version    = "7.12.0"

stacks/nextcloud/chart_values.yaml

@@ -64,6 +64,7 @@ externalDatabase:
   database: nextcloud
   existingSecret:
     secretName: nextcloud-db-creds
+    usernameKey: db-username
     passwordKey: DB_PASSWORD
 
 persistence:

stacks/nextcloud/main.tf

@@ -82,6 +82,7 @@ resource "kubernetes_manifest" "db_external_secret" {
         template = {
           data = {
             DB_PASSWORD = "{{ .password }}"
+            db-username = "nextcloud"
           }
         }
       }