Review GA implementation

[rmccar]

The way that we have set up Google Analytics is slightly different to how Google recommends in these two ways:

• This line in the analytics file is directly sending data to the dataLayer rather than using the gtag function to do it.
• The format of the data we send doesn't include an event, like what is recommended here in the GA documentation. Our data is still being sent to the dataLayer but not inside of a custom event. This may improve the data that is collected and analysed by GA. To implement this we would need to potentially prefix the event name with something to avoid using reserved words as event names such as "click" and "error".

This needs some investigation into what affect making these changes has and if it improves the data that we are able to collect.

[rmccar]

There are two ways of pushing to the datalayer. Manually using dataLayer.push() or using the gtag function. I think a solution that would use the gtag function if it exists and then if it doesn't use dataLayer.push(). One solution could be to just always use gtag but if it doesn't exist just initialise the function which will then just use dataLayer.push() within it.