template: make an explicit closure for formatting entry in peerurls This is about to be become significantly more complicated as `ui.path[x]` will become a list. Differential Revision: https://phab.mercurial-scm.org/D10443

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "phabricator.uri": "https://phab.mercurial-scm.org/",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}