We've had people who get the impression that well-known = bad,
DNS SRV = good, and who try to use DNS SRV for server delegation.

While it's true that DNS SRV can be superior for high-availability
scenarios, it's much harder to set up and comes with its own potential
downsides.

Using the well-known method is more straightforward and is enough
for almost all of us. Throwing people into the deep for no good
reason is not nice. Hopefully wording is better after this patch.

Fix concatenation of additional databases

Otherwise the postgres upgrade fails with the following error:

Unexpected templating type error occurred on ({{
  [matrix_postgres_connection_username]
  +
  matrix_postgres_additional_databases|map(attribute='username')
}}
): can only concatenate list (not "generator") to list

Fixes a problem like this:
> File "/usr/lib/python3.8/site-packages/mautrix/bridge/e2ee.py", line 79, in __init__
> raise RuntimeError("Unsupported database scheme")

mautrix-python's e2ee.py module expects to find `postgres://` instead of
`postgresql://`.

This is 8b6174786b done right. There were many more fields
that we had to account for.

Use role relative paths for references to matrix-postgres role

This makes the `sqlite://` URI match what we were using before
and what the config expects.

Some Ansible installations choke on it, it seems.
Similar to 9f00970c90

Update updating-users-passwords.md

We've hit this problem before as well. Certain Ansible installations
choke on it.

Fixed markdown error

Related to
- https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/740
- https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/686

postgres: create databases for all services

Update element-web (1.7.15 -> 1.7.16)

Update nginx (1.19.5 -> 1.19.6)

Our old (base-path -> data-path) SQLite migration can't work otherwise.

It's probably not necessary to keep it anymore, but since we still do,
at least we should take care to ensure it works.

Should have been part of 149872e00c

add option to disable nginx access log

This also adds support for installing python3-docker (not python-docker)
in systems that run Python 3.

Raspbian doesn't seem to support arm64, so this is somewhat pointless
right now.

However, they might in the future. Doing this should also unify us
some more with `setup_debian.yml` with the ultimate goal of
eliminating `setup_raspbian.yml`.

It's likely installed by default, but it doesn't hurt to specify it.
It also makes us more the same with `setup_debian.yml`.

Well, `ubuntu` or `debian`, the same key is served right now,
so it doesn't really matter.

This seems cleaner and less prone to breakage though.

Until now, we've only supported non-amd64 on Raspbian.

Seems like there are now people running Debian/Ubuntu on ARM,
so we were forcing them into amd64 Docker packages.

I've gotten a report that this change fixes support
for Ubuntu Server 20.04 on RPi 4B.