patch 9.1.0655: filetype: goaccess config file not recognized

patch 9.1.0655: filetype: goaccess config file not recognized

Problem:  filetype: goaccess config file not recognized
Solution: detect 'goaccess.conf' as goaccess filetype, also
          include a basic syntax and ftplugin (Adam Monsen)

Add syntax highlighting for GoAccess configuration file.

GoAccess is a real-time web log analyzer and interactive viewer that
runs in a terminal in *nix systems or through your browser.

GoAccess home page: https://goaccess.io

closes: #15414

Signed-off-by: Adam Monsen <haircut@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>