Missing data in contexts for MariaDB

[williamdes]

While discovering the parser I started to wrongly add implementations, they never where pushed but here are some commit lines that pinpoint missing MariaDB commands

• Add new "BACKUP {LOCK,UNLOCK}" commands on MariaDB >= 10.4.2
• Add new "BACKUP STAGE {START,FLUSH,BLOCK_DDL,BLOCK_COMMIT,END}" commands on MariaDB >= 10.4.1
• Add new command "FLUSH SSL" on MariaDB >= 10.4