chore(images): pin service image updates

Replace floating service images with reviewable tags or digests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

authentik/k8s/postgresql.yaml

@@ -29,7 +29,7 @@ spec:
     spec:
       containers:
         - name: postgres
-          image: docker.io/library/postgres:15-alpine
+          image: docker.io/library/postgres:15.19-alpine
           env:
             - name: POSTGRES_DB
               value: authentik