Add additional tracking information to mediawiki.searchSuggest

Add additional tracking information to mediawiki.searchSuggest

Adds a few pieces of information to improve tracking of autocomplete
usage.

* When using Special:Search 'go' feature forward wprov parameter to redirect
* Include a data attribute indicating autocomplete location to
  differentiate usage of the header and Special:Search content autocompletes
* Report exact query string that was used for impression-results
* Add handling to allow searchSuggest subscribers to append tracking
  information to generated article links
* Add a new hook, SpecialSearchGoResult, that can either change the url
  redirected to in the 'go' feature or cancel it entirely.

Bug: T125915
Change-Id: Iec7171fcf301f1659d852afa87ce271f468177c1