Make sure that we have a `server_notices_mxid` set, given that we are relying
on it.

* Set allow_guest_access = True, since we rely on it
* config doesn't have a `hostname` attribute; it is `server_name`

The Mailer expects the config object to have `email_smtp_pass` and
`email_riot_base_url` attributes (and it won't by default, because the default
config impl doesn't set any of the attributes unless email_enable_notifs is
set).

Fixes a bug where hs_disabled_message was not enforced for 3pid-based requests
if there was no server_notices_mxid configured.

Make it so that most options in the config are optional, and commented out in
the generated config.

The reasons this is a good thing are as follows:

* If we decide that we should change the default for an option, we can do so,
  and only those admins that have deliberately chosen to override that option
  will be stuck on the old setting.

* It moves us towards a point where we can get rid of the super-surprising
  feature of synapse where the default settings for the config come from the
  generated yaml.

* It makes setting up a test config for unit testing an order of magnitude
  easier (see forthcoming PR).

* It makes the generated config more consistent, and hopefully easier for users
  to understand.

Add two ratelimiters on login (per-IP address and per-userID).

Split TransactionQueue up

Move client receipt processing to federation sender worker.

Allow passing --daemonize to workers

This setup is a way to manage workers with systemd. It does however not
require workers. You can use this setup without workers. You just have
to make sure that the homeserver is forking and writes its PID file
to the location the service is looking in.

The currently distributed setup in the debian package does not work in
conjunction with workers.

* Adds changelog

* Lets systemd handle the forking

Sets all services to `type=simple` and disables daemonizing on the
synapse side.

* Formats readme to 80 columns per line

* Allows for full restart of all workers

* Changes README to reflect the new setup

* Adds dot to end of changelog file

* Removes surplus word

Co-Authored-By: targodan <targodan@users.noreply.github.com>

* Adds missing word

Co-Authored-By: targodan <targodan@users.noreply.github.com>

* Fixes linebreak

Co-Authored-By: targodan <targodan@users.noreply.github.com>

* Fixes unit type

* Add some stuff back to the .gitignore

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Add changelog

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Reorder and remove old items from .gitignore

Signed-off-by: Aaron Raimist <aaron@raim.ist>

Revert "Make federation endpoints more tolerant of trailing slashes for some endpoints"

This reverts commit 290552fd.

Improve searching in the userdir

This is easier than having to have a million fields keyed on destination.

This is mostly a prerequisite for #4730, but also fits with the general theme
of "move everything off the master that we possibly can".

I'm going to use this in queues and things, so it'll be useful to give it more
of a structure.

Transfer push rules (notifications) on room upgrade

Improved federation configuration docs.  Specifically detailing  .well-known and SRV based delegation methods. 

Inspiration Valentin Lab <valentin.lab@kalysto.org> for https://github.com/matrix-org/synapse/pull/4781