localrepo: add repository feature when repo can be stream cloned
Right now, the wire protocol server assumes all repository objects can
be stream cloned (unless the stream clone feature is disabled via
config option).
But not all storage backends or repository objects may support stream
clone.
This commit defines a repository feature denoting whether stream clone
is supported. The feature is defined for revlog-based repositories,
which should currently be "all repositories."
Differential Revision: https://phab.mercurial-scm.org/D4852
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}