message: Expose max_allowed_packet to env vars.
  Allows max_allowed_packets to be overridden with an env var.
diff: @@ -21,7 +21,7 @@ innodb_log_buffer_size = 32M
  innodb_log_file_size = ${MARIADB_INNODB_LOG_FILE_SIZE:-64M}
  join_buffer_size = 2M
  key_buffer_size = 16M
  -max_allowed_packet = 64M
  +max_allowed_packet = ${MARIADB_MAX_ALLOWED_PACKET:-64M}
  max_binlog_size = 100M
  max_connections = 400
  max_heap_table_size = 512M
  