Suggest people use a config file for Docker instead of env vars

Fixes #5602, #5603

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

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

* SAML2 Improvements and redirect stuff

Signed-off-by: Alexander Trost <galexrt@googlemail.com>

* Code cleanups and simplifications.

Also: share the saml client between redirect and response handlers.

* changelog

* Revert redundant changes to static js

* Move all the saml stuff out to a centralised handler

* Add support for tracking SAML2 sessions.

This allows us to correctly handle `allow_unsolicited: False`.

* update sample config

* cleanups

* update sample config

* rename BaseSSORedirectServlet for consistency

* Address review comments

Fix --no-daemonize flag for synctl

Signed-off-by: Amir Zarrinkafsh <nightah@me.com>

Signed-off-by: Pau Rodriguez-Estivill <prodrigestivill@gmail.com>

Fixes #5582

Fix sync tightloop bug.

Don't update the ratelimiter before sending a 3PID invite

If we do the opposite, an event can arrive after or while sending the email and the 3PID invite event will get ratelimited.

This would cause emails being sent, but Synapse responding with a 429 when creating the event. The client would then retry, and with bad timing the same scenario would happen again. Some testing I did ended up sending me 10 emails for one single invite because of this.

Signed-off-by: Daniel Hoffend <dh@dotlan.net>

Signed-off-by: Silke Hofstra <silke@slxh.eu>

Helps address #5444

Refactor devices changed query to pull less from DB

... to help people escape env var hell

There's not much point in binding to localhost when it's in a docker container.

This is mostly a documentation change, but also adds a default value for
SYNAPSE_CONFIG_PATH, so that running from the generated config is the default,
and will Just Work provided your config is in the right place.

* Fix JWT login with register

Signed-off-by: Pau Rodriguez-Estivill <prodrigestivill@gmail.com>

* Add pyjwt conditional dependency

Signed-off-by: Pau Rodriguez-Estivill <prodrigestivill@gmail.com>

* Added changelog file

Signed-off-by: Pau Rodriguez-Estivill <prodrigestivill@gmail.com>

* Improved changelog description

Signed-off-by: Pau Rodriguez-Estivill <prodrigestivill@gmail.com>

Docker: generate our own log config

this makes docker builds a bit faster.

Docker image: add support for SYNAPSE_DATA_DIR parameter