Add submodule for PHP version, MySQL version, etc

This was originally requested as part of a Tech Drop-in chat for LocalGov Drupal.

Let's hope people are careful about what users can view this data - we don't necessarily want _everyone_ knowing what out-of-date version a a database you are using for example.

I'm also starting to think if we want this, it should be a standalone module rather than part of the Modules List module. I'm not sure this json feed has much to do with "Modules List".