Access gtag instance directly

I try to make all method a bit simpler so you don't need extra boilerplate, but gtag api is quite vast, so in case you didn't find what you were looking for, you can use the query method: it's like using gtag itself.

export default {
name: 'MyComponent',
methods: {
track () {
this.$gtag.query('event', 'screen_view', {
app_name: 'MyApp',
screen_name: 'Home page',