Track Lunr search-result clicks

[chalin]

Tasks

• [x] Use link_url as parameter key instead of value; for details about click event parameters see [GA4] Analytics dimensions and metrics > Analytics dimensions > Links - #1571
• [x] Also set outbound to false while we're at it - #1571
• [ ] Investigate other ways to identify search-result URL visits, such as using query parameter(s)

Context

Originally posted by @harshit-gangal in https://github.com/vitessio/website/pull/1519#discussion_r1304687307

The statement you are referring to (https://developers.google.com/tag-platform/devguides/events#gtag.js_1) concerns UA:

The Universal Analytics event information is structured as follows: <value> ... A non-negative integer that will appear as the vent value.

I'm not aware that this is a restriction for GA4. In fact, you can see the search-result URL from the realtime event reports page as the value of the value attribute. For this example, I searched for "install" and clicked on the "Local Install via Homebrew" search result:

Also, by using the tagassistant, you can see that the search-result URL is available as ep.value of a click event:

Name	Parameter	Value
Protocol Version	v	2
Measurement ID	tid	G-JWT03RNV4P
Page Title	dt	Vitess | Scalable. Reliable. MySQL-compatible. Cloud-native. Database.
Event Name	en	click
Event Parameter	ep.anonymize_ip	false
Event Parameter	ep.event_category	Lunr Search
Event Parameter	ep.event_label	Search-result Click
Event Parameter	ep.search_term	install
Event Parameter	ep.value	https://vitess.io/docs/17.0/get-started/local-mac/

That being said, it will be difficult to use GA4 reports to view the URL. Let me investigate this further.

[chalin]

For a search-result click event, it would be better to use link_url rather than value to hold the search-result URL. Let me make that change first. Note that even with that change, I haven't been able to generate reports containing that URL, despite adding custom metrics. (Maybe it's just because custom reports don't have access to realtime data, so I'll try again tomorrow.)

[chalin]

Yesterday I defined some custom metrics (see below), but it seems that only restricted metric types are supported, excluding strings:

The custom metrics (set to type "standard") turn out to be interpreted as integers in reports: