narrow: move the ellipses server capability to core
This will be used in core logic to determining whether a server is ellipses
enabled or not. And also this will ease moving narrow related things to core.
Differential Revision: https://phab.mercurial-scm.org/D4809
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}