Add the PostHog script (#194)

Update main.html

documentation/_resource/overrides/main.html

@@ -26,6 +26,10 @@
                  <meta property="og:title" content="{{ title }}" />
                  <meta property="og:image" content="https://docs.percona.com/pg-stat-monitor/_images/pg_stat_monitor.png">
                  <meta property="og:url" content="https://docs.percona.com/pg-stat-monitor/">
+    <script>
+        !function(t,e){var o,n,p,r;e.__SV||(window.posthog=e,e._i=[],e.init=function(i,s,a){function g(t,e){var o=e.split(".");2==o.length&&(t=t[o[0]],e=o[1]),t[e]=function(){t.push([e].concat(Array.prototype.slice.call(arguments,0)))}}(p=t.createElement("script")).type="text/javascript",p.async=!0,p.src=s.api_host+"/static/array.js",(r=t.getElementsByTagName("script")[0]).parentNode.insertBefore(p,r);var u=e;for(void 0!==a?u=e[a]=[]:a="posthog",u.people=u.people||[],u.toString=function(t){var e="posthog";return"posthog"!==a&&(e+="."+a),t||(e+=" (stub)"),e},u.people.toString=function(){return u.toString(1)+".people (stub)"},o="capture identify alias people.set people.set_once set_config register register_once unregister opt_out_capturing has_opted_out_capturing opt_in_capturing reset isFeatureEnabled onFeatureFlags getFeatureFlag getFeatureFlagPayload reloadFeatureFlags group updateEarlyAccessFeatureEnrollment getEarlyAccessFeatures getActiveMatchingSurveys getSurveys onSessionId".split(" "),n=0;n<o.length;n++)g(u,o[n]);e._i.push([i,s,a])},e.__SV=1)}(document,window.posthog||[]);
+        posthog.init('phc_7unoI9J6Fm0SMrfDp35xNOpCRTkOAibbffQwdGWbHnL',{api_host:'https://eu.posthog.com'})
+    </script>
               {% endblock %}