UI Enhancement: Offer hint when user attempts to create Segment Contains URL

[atom-box]

Scope: This is in the Top 10 most common confusions about Segments

What happens:
The user creates a segment: Segment URL contains www.example.com/123.
The user opens Matomo >> Behavior >> Pages.
They see many pages, not only one page*.
They write to Matomo: "Segment is broken: it gives several URLs when I intend to only see one URL".

What should happen:
A hint should pop up: "It looks like you are trying to make a segment to analyze behavior of a particular page. This information already exists as a report in Matomo: Behavior >> Transitions. Or a different approach, if you have the feature Custom Reports, is to add the URL as a filter to any Custom Report." The pop up would just have a "dismiss" button and a link to the faqs for Transitions.

*This is by design, but still it is an impediment. This well-known "gotcha" is caused by Matomo's data being Visit-based, not Event-based

[sgiehl]

@atom-box The problem is that people are mixing up things and might have different expectations. In general our segments are visit base. Event based segments wouldn't make too much sense.
In certain cases customers expect segments to act as filters (see #15438) - but only for certain reports.
We need to find a good way to help all users understand how segments work in general and what they can expect from it. I don't think it's helpful to display hints only if certain segment conditions are chosen.
Maybe another thing to consider would be changing the naming / description of all action base segments, so it's directly clear, that those segments will be used to look for matching visits, rather than filtering.