Allow tracking UTM parameters properly

[sneko]

Hi,

There are multiple reasons the frontend can loose UTM parameters on a SPA frontend (redirection at init, user accepting tracking X minutes after...). So I decided to create a new library to gather those basic methods in response to #351 and #405 (comment) (and other issues for other frameworks/plugins).

Everything can be read at https://github.com/sneko/utm-synapse

This PR makes this repo now having a dependency (sorry)... but I felt it better to use a new package for this since it could be reused by others in their project (none-Vue but also none-gtag projects).

To use it the just enable the features inside the config:

    appName: 'hello',
    trackInitialUtmParams: true,
    hideInitialUtmParams: true,

Since PRs stack up (I can understand it's hard to maintain the library on your spare time) I copied all your deployment logic so my modified package is released and available through yarn add @sneko/[email protected](see https://github.com/sneko/vue-gtag/tree/v1.17.2)

Hope it can help!