Add rule to check the usage of the Content-Type HTTP response header

[alrra]

• Check if resources are served with correct media type.

  Note: In most cases the media type doesn’t matter, browser sniff the content, or simply don't care, but in some (e.g. 1, 2) they do!

• Check if the charset parameter (i.e.: Content-Type:"text/html; charset=utf-8") is specified for text resources (e.g.: HTML, JS, CSS, JSON, XML, VTT, manifest files, etc.)