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/restore.md

@@ -45,9 +45,9 @@ services:
       - DB_PORT=3306
       - DB_HOST=postgres
       - DB_NAME=database
-      - DB_USERNAME=username
+      - DB_USER=username
       - DB_PASSWORD=password
-    # Ensure the pg-bkup container is connected to the same network as your database
+    # Ensure the mysql-bkup container is connected to the same network as your database
     networks:
       - web