Add instructions for authorization header under Apache

[SimonFrings]

This pull requests adds an additional line of configuration to the .htaccess file to support authorization headers under Apache.

I ran into this problem when I was setting up a new project which sets the HTTP Authorization header. It seems like Apache does not pass the Authorization header by default, because the default setting for the CGIPassAuth is Off, according to Apache's documentation. The same issue has been reported in several forums e.g. this one on stackoverflow.

Adding these instructions to the .htaccess causes the authorization header to be passed along 👍

Inside our acceptance tests we're using the php docker image which has special configuration settings for Apache, thus sending the Authorization header along without any additional adjustments needed.

[clue]

@SimonFrings Thanks for looking into this, changes LGTM!