Add basic health check for db container

compose.yml

@@ -87,6 +87,12 @@ services:
         backupbot.backup.path: "/tmp/backup/"
         backupbot.restore: "true"
         backupbot.restore.post-hook: "sh -c 'psql -U $${POSTGRES_USER} -d $${POSTGRES_DB} < ./backup.sql && rm -f ./backup.sql'"
+    healthcheck:
+      test: "pg_isready"
+      interval: 30s
+      timeout: 10s
+      retries: 5
+      start_period: 1m
 volumes:
   postgres:
   codimd_uploads: