Create a page for CONNECT table type XML

Here is the page with CONNECT engine table types:

https://mariadb.com/kb/en/connect/

It does not offer any information about XML type, and the summary page only says that it exists.

I don't know much about the type, but what I find important to document (at least) is that it requires certain things to be installed; I had to install libxml2-dev. It also has quite a few table options, so it definitely deserves a dedicated page.