* Port synapse.replication.tcp to async/await

* Newsfile

* Correctly document type of on_<FOO> functions as async

* Don't be overenthusiastic with the asyncing....

Cleanups and additions to the module API

Allow REST endpoint implemnentations to raise a RedirectException, which will
redirect the user's browser to a given location.

Currently we rely on `current_state_events` to figure out what rooms a
user was in and their last membership event in there. However, if the
server leaves the room then the table may be cleaned up and that
information is lost. So lets add a table that separately holds that
information.

This means that things like to device messages don't get blocked behind
processing PDUs, which can potentially take *ages*.

This is pretty pointless. Let's just use SynapseError.

Fix a bug where we would assign a numeric userid if somebody tried registering
with an empty username

Updates to the SAML mapping provider API

AdditionalResource really doesn't add any value, and it gets in the way for
resources which want to support child resources or the like. So, if the
resource object already implements the IResource interface, don't bother
wrapping it.

Fixes #6402

... for consistency with other modules, and because we'll need it sooner or
later and it will be a pain to introduce later.

Some modules don't need any config, so having to define a `config` property
just to keep the loader happy is a bit annoying.

Add some useful things, such as error types and logcontext handling, to the
API.

Make `hs` a private member to dissuade people from using it (hopefully
they aren't already).

Add a couple of new methods (`record_user_external_id` and
`generate_short_term_login_token`).

Refuse to start if sqlite is older than 3.11.0

this saves doing it on each connection, and will allow us to pass extra options
in.

We might not need the cursor at all.

Signed-off-by: Manuel Stahl <manuel.stahl@awesome-technologies.de>

Fix media repo admin APIs when using a media worker.