Revert plugins API htaccess update and add an htaccess files to be located in the old documentation folder

We should avoid having a huge .htacess in the root directory and instead have the API .htaccess files with the right content in /srv/gstreamer.freedesktop.org/www/data/doc/gstreamer/head/.htaccess and /srv/gstreamer.freedesktop.org/www/data/doc/gstreamer/stable/.htaccess

I am not sure it is the way to do that, I places the .htaccess there manually and it works, do we have risk to have them overwritten?