add gtag configuration (#119)

Co-authored-by: HEREYUA <1240335630@qq.com>
Reviewed-on: https://gitea.com/gitea/gitea-docusaurus/pulls/119
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: liuyu <liuyu@noreply.gitea.com>
Co-committed-by: liuyu <liuyu@noreply.gitea.com>

docusaurus.config.js

@@ -138,6 +138,9 @@ const config = {
           customCss: require.resolve('./src/css/custom.css'),
         },
         pages: pageConfig,
+        gtag: {
+          trackingID: 'G-KHM0KYT506'
+        },
       }),
     ],
     apiConfig,