This patch adds support for the endpoints used in [MSC3814].
One notable change to the MSC here is that the PUT endpoint uploads the
device and one-time keys as well.
[MSC3814]: https://github.com/matrix-org/matrix-spec-proposals/pull/3814
Co-authored-by: Kévin Commaille <76261501+zecakeh@users.noreply.github.com>
