Wish: Add mysql example

[stappersg]

This issue is to express the wish that actix-web get a mysql example

Like #397 and #405 is this issue tagged new-example.

I'm aware of mariadb, reason for having mysql in the issue title is that the protocol is named mysql.

And I hope that this issue attracts messages like "At some_URL is the combo actix-web and mysql being used"