* 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>

Related to:

- https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1727
- https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1754
- https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1755
- https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/467

As mentioned in the changelog, this is a breaking change.

This announces matrix-hookshot support that got added in
https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1505

Playbook config copied from mautrix-facebook and altered accordingly.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1055

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/962

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/683

instead of bullet points which make it more difficult to tell whether or not you completed all of the steps

Prompted by this: https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/779#issuecomment-764807507

Fixes #562 (Github Issue)

Fixes #586 (Github Issue)

Related to #557 (Github Pull Request).

Related to #540 (Github Pull Request).

Related to #551 and #555 (Github Pull Requests).

added docs, added seperate service for database, pr comments

Related to #454 (Github Pull Request).

Related to #339 (Github Pull Request).

Fixes #255 (Github Issue).

Fixes #71 (Github Issue).