BootTrait - Define a preference for absolute URLs in default://

[totten]

This patch (in combination with civicrm/civicrm-core#26861) allows cv to pick URLs based on their metadata

Compare:

## Link to "civicrm/admin", which is declared as is_public=0
$ cv ev 'return Civi::url("//civicrm/admin");'
"http://wpmaster.127.0.0.1.nip.io:8001/wp-admin/admin.php?page=CiviCRM&q=civicrm%2Fadmin"

## Link to "civicrm/user", which is declared as is_public=1
$ cv ev 'return Civi::url("//civicrm/user");'
"http://wpmaster.127.0.0.1.nip.io:8001/civicrm/?civiwp=CiviCRM&q=civicrm%2Fuser"