remotenames: mark the extension as EXPERIMENTAL I still don't feel confident about locking the behavior of all the things in the remotenames extension. Moreover the extension was introduced in this cycle only. Let's mark this extension EXPERIMENTAL for now so that we can change things especially the storage layer if required in next cycle. I will like to use cbor at storage layer too. Differential Revision: https://phab.mercurial-scm.org/D3426