feat: mysql-bkup v2 on bkupkit

MysQL backup and restore built on the shared bkupkit core:
streaming end to end, with no dump held in memory or written to
local disk.

docs/how-tos/backup-to-ftp.md

@@ -50,10 +50,10 @@ services:
       - DB_PORT=3306
       - DB_HOST=mysql
       - DB_NAME=database
-      - DB_USERNAME=username
+      - DB_USER=username
       - DB_PASSWORD=password
       ## FTP Configuration
-      - FTP_HOST="hostname"
+      - FTP_HOST=hostname
       - FTP_PORT=21
       - FTP_USER=user
       - FTP_PASSWORD=password