[Etherpad] Try to optimize database

pica-etherpad/docker-compose.yml

@@ -51,5 +51,7 @@ services:
       - etherpad-db-volume:/var/lib/mysql
     env_file: ./secrets/etherpad-db.secrets
     restart: unless-stopped
+    # See https://stackoverflow.com/questions/41134785/how-to-solve-mysql-warning-innodb-page-cleaner-1000ms-intended-loop-took-xxx
+    command: --innodb_lru_scan_depth=128
     networks:
       - docker_default