chore(deps): update ghcr.io/stalwartlabs/stalwart docker tag to v0.15.0

Author: renovate[bot]

docker-compose.yml

@@ -318,7 +318,7 @@ services:
     restart: unless-stopped
 
   stalwart:
-    image: ghcr.io/stalwartlabs/stalwart:v0.14.1-alpine
+    image: ghcr.io/stalwartlabs/stalwart:v0.15.0-alpine
     hostname: ${STALWART_DOMAIN:-stalwart.opencloud.test}
     depends_on:
       opencloud: