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>

src/testdir/test_filetype.vim

@@ -300,6 +300,7 @@ def s:GetFilenameChecks(): dict<list<string>>
     gnash: ['gnashrc', '.gnashrc', 'gnashpluginrc', '.gnashpluginrc'],
     gnuplot: ['file.gpi', '.gnuplot', 'file.gnuplot', '.gnuplot_history'],
     go: ['file.go'],
+    goaccess: ['goaccess.conf'],
     gomod: ['go.mod'],
     gosum: ['go.sum', 'go.work.sum'],
     gowork: ['go.work'],