Remove code invalidated by deprecated config flag 'trust_identity_servers_for_password_resets' (#11395)

* remove background update code related to deprecated config flag

* changelog entry

* update changelog

* Delete 11394.removal

Duplicate, wrong number

* add no-op background update and change newfragment so it will be consolidated with associated work

* remove unused code

* Remove code associated with deprecated flag from legacy docker dynamic config file

Co-authored-by: reivilibre <oliverw@matrix.org>

Setting the value will help PostgreSQL free up memory by recycling
the connections in the connection pool.

Signed-off-by: Toni Spets <toni.spets@iki.fi>

Part of #9744

Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.

`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl&gt;`>

Signed-off-by: Dan Callahan <danc@element.io>

`room_invite_state_types` was inconvenient as a configuration setting, because
anyone that ever set it would not receive any new types that were added to the
defaults. Here, we deprecate the old setting, and replace it with a couple of
new settings under `room_prejoin_state`.

`uploads_path` was a thing that was never used; most of it was removed in #6628
but a few vestiges remained.

 - Update black version to the latest
 - Run black auto formatting over the codebase
    - Run autoformatting according to [`docs/code_style.md
`](https://github.com/matrix-org/synapse/blob/80d6dc9783aa80886a133756028984dbf8920168/docs/code_style.md)
 - Update `code_style.md` docs around installing black to use the correct version

This breaks some people's configurations (if their Client-Server API
is not accessed via port 443).

Fixes #8928.

This is now only used in `test_typing`, so move it there.

Changes `@cache_in_self` to use underscore-prefixed attributes.

This implements a more standard API for instantiating a homeserver and
moves some of the dependency injection into the test suite.

More concretely this stops using `setattr` on all `kwargs` passed to `HomeServer`.

This is so we can tell what is going on when things are taking a while to start up.

The main change here is to ensure that transactions that are created during startup get correctly logged like normal transactions.

This ended up being a bit more invasive than I'd hoped for (not helped by
generic_worker duplicating some of the code from homeserver), but hopefully
it's an improvement.

The idea is that, rather than storing unstructured `dict`s in the config for
the listener configurations, we instead parse it into a structured
`ListenerConfig` object.

By persisting the user interactive authentication sessions to the database, this fixes
situations where a user hits different works throughout their auth session and also
allows sessions to persist through restarts of Synapse.

When running the UTs against a postgres deatbase, we need to set the collation
correctly.

* Pull Sentinel out of LoggingContext

... and drop a few unnecessary references to it

* Factor out LoggingContext.current_context

move `current_context` and `set_context` out to top-level functions.

Mostly this means that I can more easily trace what's actually referring to
LoggingContext, but I think it's generally neater.

* move copy-to-parent into `stop`

this really just makes `start` and `stop` more symetric. It also means that it
behaves correctly if you manually `set_log_context` rather than using the
context manager.

* Replace `LoggingContext.alive` with `finished`

Turn `alive` into `finished` and make it a bit better defined.

This is so that we don't have to rely on pulling it out from `current_state_events` table.

This encapsulates config for a given database and is the way to get new
connections.

The expected use case is to suppress MAU limiting on small instances