Fix typo in _select_thumbnail

These now exist in the pipelines repo.

The old statement returned `None` for such a `password_config` (like the one
created on first run), thus retrieval of the `pepper` key failed with
`AttributeError`.

Fixes #5315

Signed-off-by: Ivan Vilata i Balaguer <ivan@selidor.net>

* Raise an exception if there are pending background updates

So we return with a non-0 code

* Changelog

* Port synapse_port_db to async/await

* Port update_database to async/await

* Add version string to mocked homeservers

* Remove unused imports

* Convert overseen bits to async/await

* Fixup logging contexts

* Fix imports

* Add a way to print an error without raising an exception

* Incorporate review

Co-Authored-By: Erik Johnston <erik@matrix.org>

This reverts commit 11c23af4.

So we can debug issues like #6683 more easily

Fix #6727
Related #6655

Co-authored-by: Erik Johnston <erikj@jki.re>

Fix instantiation of message retention purge jobs

Log saml assertions rather than the whole response

Turns out that figuring out a remote user id for the SAML user isn't quite as obvious as it seems. Factor it out to the SamlMappingProvider so that it's easy to control.

This will be used to retry outbound transactions to a remote server if
we think it might have come back up.

Generally try to make this more comprehensible, and make it match the
conventions.

I've removed the documentation for all the settings which allow you to change
the names of the template files, because I can't really see why they are
useful.

... since the whole response is huge.

We even need to break up the assertions, since kibana otherwise truncates them.