added matomo dev option

frontend/gatsby-config.js

@@ -22,7 +22,8 @@ module.exports = {
       options: {
         siteId: process.env.MATOMO_ID || '53',
         matomoUrl: process.env.MATOMO_URL || 'https://stats.waag.org/',
-        siteUrl: 'https://prototype.openschoolingnavigator.eu/'
+        siteUrl: 'https://prototype.openschoolingnavigator.eu/',
+        dev: process.env.MATOMO_DEV === "TRUE"
       }
     },
     {