Add the ability to activate tours by URL part

There should be a field in the JSON that can be a regex or a simple string and the tour will be only offered on URLs that match the Regex or contain the string.

Use case for Polyglots: have language specific tours on pages like https://make.wordpress.org/polyglots/teams/?locale=de_DE that don't have a CSS class that allows differentiation.

No file or test entry point is named in the issue; begin by tracing how tour JSON is loaded and how the current page URL determines whether a tour is offered. Done means a tour condition can use either a regex or substring and can distinguish the Polyglots locale URL example.

Written by the indexing model from the issue text.