.. regardless of whether matrix-nginx-proxy runs in a container or not

When setting `matrix_nginx_proxy_enabled: false` and enabling authentication on the metrics endpoint, the htpasswd file is hardcoded to the nginx-proxy container dir, this changes the hardcoded value to a variable so the path can be updated

According to https://signald.org/articles/install/docker/#migrating-from-versions-before-0180,
This release only chowns files if the container is running as root. See also this upstream commit:
3bb7e8d2c1

The maunium fork of Signald is no longer up-to-date (does not publish
0.18.0.. at least not yet) and all the necessary changes are now upstream.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1775

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1775

Related to https://signald.org/articles/install/docker/#migrating-from-versions-before-0180

> Prior to 0.18.0 the signald container image used the root user, which is not recommended for security reasons. This was fixed in the 0.18.0 release which will start as root, fix permissions on the volume, then drop to the non-root user and start signald. Future images will start as the non-root user, so if you’re upgrading make sure to run 0.18.0 at least once.
> A special tag, 0.18.0-non-root, will be published. it starts as the non-root user and does not fix permissions on the volume.

This reverts commit 986fe779cd.

The error was: error while evaluating conditional: 'matrix_synapse_s3_media_store_enabled' is undefined

This reverts commit a31017d716.

* Add matrix-registration-bot

This adds an install and uninstall task plus helpers. The bot is disabled by default.
This commit does not include documentation, yet. In short, the bot can be enabled by adding
matrix_bot_matrix_registration_bot_enabled: true
matrix_bot_matrix_registration_bot_matrix_user_password: "verysecret"
matrix_bot_matrix_registration_bot_matrix_admin_token: "supersecret"
to the host_vars

* Change bot username to bot.matrix-registration-bot following convention

* Address smaller remarks, fix local docker build

* Switch to an env file

* Add environment variables extension for additional config

* Add documentation for the matrix-registration-bot

* Add screenshot on how to obtain admin access token

* Use bot as admin to only have one access token (bot and admin api)

* Use cleaner setting of matrix_synapse_registration_requires_token

* Use config file for cleaner more secure usage

* Delete unneeded env

* Rename vars to make usage clear

* Fix typos/wording and add notice about logging out

* Convert configuration to use |to_json

* Reorder role includes

Nothing should be after `matrix-common-after`.

`matrix-bot-matrix-registration-bot` can probably be anywhere, but it makes sense to put it next to the other `matrix-bot-*` roles.

* Minor group_vars/matrix_servers touchups

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

Comments taken from https://github.com/matrix-org/matrix-appservice-slack/blob/develop/config/config.sample.yaml

We should probably reconcile our configuration with that one and include comments for other fields as well.

It is very confusing to debug why messages only go from Matrix to Slack
but not from Slack to Matrix. RTM should be enabled by default, as
that's the recommended way to make this work.