Add GA tracking events

[kammerer]

For impact capture, I recommend adding in Google Analytics
conversion tracking tags to the key parts of the page, such as the
“Search” button – when someone uses the portal to search, this
will fire a conversion event, letting you know someone got use from
it. There are several others, all are minor code amends to the page,
the rest I can configure straight from the analytics interface. Other
good things to track are when people login with orcid, click “Browse
data” or “submit data” etc, or even email you for support.
Documentation for this implementation is here:
https://developers.google.com/analytics/devguides/collection/analyticsjs/events
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