clonebundle: add a `filter_bundle_url` function This function does nothing by default, but give extension the opportunity to alter the URL, typically, this could be used to inject authentication token when serving clone bundle for private repositories.

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