... 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.

When running under docker, we want to use docker's own logging stuff rather
than losing the logs somewhere on the container's filesystem, so let's use log
configs that spit logs out to stdout instead.

Fixes #4830.

We don't want to generate any missing configs when running from a precanned
config.

(There's a strong argument that we don't want to do this at all, since
generating a new signing key on each invocation sounds disasterous, but I don't
fancy unpicking that for now.)

... and inline generate_secrets

Fixes #3370.

Python 3.7 is apparently faster than 3.6, and should be mature enough.

Fixes #5467.

because this file is reproduced on dockerhub and relative paths don't work

Add missing backslash

psycopg 2.8 is now out, which means that the C library gets built from source,
so we now need libpq-dev when building.

Turns out the need for this package is already documented in
docs/postgres.rst.

Using systemd-python allows for logging to the systemd journal,
as is documented in: `synapse/contrib/systemd/log_config.yaml`.

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

Correct default POSTGRES_USER in Docker README

Signed-off-by: Jurrie Overgoor <1213142+Jurrie@users.noreply.github.com>

Signed-off-by: Jurrie Overgoor <1213142+Jurrie@users.noreply.github.com>

Make sure it refreshes the apt cache before trying to install stuff

* 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

There are two reasons this is a good thing:

 * first, it means that you don't end up with stuff kicking around your working
   copy ending up in the build image by mistake (which can upset the pip
   install process)

 * second: it means that the docker image cache is more effective, and we can
   reuse docker images when iterating on the docker stuff.

* remove dh_params and set better cipher string

Rewrite this in python so that it can be run in parallel.

since #4298, the optional dependencies are no longer installed with a simple
`pip install .`, which meant that they were not being included in the debian
package.

The easy fix to that is dh_virtualenv --extras, but that needs dh_virtualenv
1.1...

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

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