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>

Fixes #9778

ACME v1 has been fully decommissioned for existing installs on June 1st 2021(see https://community.letsencrypt.org/t/end-of-life-plan-for-acmev1/88430/27), so we can now safely remove it from Synapse.

Fixes #9970

Signed-off-by: Sergio Miguéns Iglesias <lonyelon@lony.xyz>

This PR adds a Dockerfile and some supporting files to the `docker/` directory. The Dockerfile's intention is to spin up a container with:

* A Synapse main process.
* Any desired worker processes, defined by a `SYNAPSE_WORKERS` environment variable supplied at runtime.
* A redis for worker communication.
* A nginx for routing traffic.
* A supervisord to start all worker processes and monitor them if any go down.

Note that **this is not currently intended to be used in production**. If you'd like to use Synapse workers with Docker, instead make use of the official image, with one worker per container. The purpose of this dockerfile is currently to allow testing Synapse in worker mode with the [Complement](https://github.com/matrix-org/complement/) test suite.

`configure_workers_and_start.py` is where most of the magic happens in this PR. It reads from environment variables (documented in the file) and creates all necessary config files for the processes. It is the entrypoint of the Dockerfile, and thus is run any time the docker container is spun up, recreating all config files in case you want to use a different set of workers. One can specify which workers they'd like to use by setting the `SYNAPSE_WORKERS` environment variable (as a comma-separated list of arbitrary worker names) or by setting it to `*` for all worker processes. We will be using the latter in CI.

Huge thanks to @MatMaul for helping get this all working  This PR is paired with its equivalent on the Complement side: https://github.com/matrix-org/complement/pull/62.

Note, for the purpose of testing this PR before it's merged: You'll need to (re)build the base Synapse docker image for everything to work (`matrixdotorg/synapse:latest`). Then build the worker-based docker image on top (`matrixdotorg/synapse:workers`). 

`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.

Replace 'perspectives' config block with 'trusted_key_servers' in docker homeserver.yaml template (#9157)

Signed-off-by: Mateusz Przybyłowicz <uamfhq@gmail.com>

We do this to prevent foot guns. The default config uses a MemoryFilter,
but users are free to change to logging to files directly. If they do
then they have to ensure to set the `filters: [context]` on the right
handler, otherwise records get written with the wrong context.

Instead we move the logic to happen when we generate a record, which is
when we *log* rather than *handle*.

(It's possible to add filters to loggers in the config, however they
don't apply to descendant loggers and so they have to be manually set on
*every* logger used in the code base)

Turns out that loggers that are instantiated before the config is loaded get
turned off.

Also bring the logging config that is generated by --generate-config into line.

Fixes #6194.

This adds a missing space, without which log lines appear uglier.

Signed-off-by: Slavi Pantaleev <slavi@devture.com>

Removes any `SMTP_*` docker container environment variables from having any effect on the default config.

Fixes https://github.com/matrix-org/synapse/issues/5430

... to help people escape env var hell

Fixes #3370.

* no_tls is now redundant (#4613)
* we don't need a dummy cert any more (#4618)

Also:

* Fix wrapping in docker readme
* Clean up some docs on the docker image
* a workaround for #4554

* remove dh_params and set better cipher string

These aren't used, because we have a `log_config` setting.

Signed-off-by: Cédric Laudrel <dek@iono.me>

move the example email templates into the synapse package so that they can be
used as package data, which should mean that all of the packaging mechanisms
(pip, docker, debian, arch, etc) should now come with the example templates.

In order to grandfather in people who relied on the templates being in the old
place, check for that situation and fall back to using the defaults if the
templates directory does not exist.

This addresses #3224