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

Signed-off-by: Tulir Asokan <tulir@maunium.net>

`matrix_container_images_self_build` was not really doing anything
anymore. It previously was influencing `matrix_*_self_build` variables,
but it's no longer the case since some time ago.

Individual `matrix_*_self_build` variables are still available.
People that would like to toggle self-building for a specific component
ought to use those.

These variables are also controlled automatically (via
`group_vars/matrix_servers`) depending on `matrix_architecture`.

In other words, self-building is being done automatically for
all components when they don't have a prebuilt image for the specified
architecture. Some components only support `amd64`, while others also
have images for other architectures.

Use playbook variables instead of textual place-holders for the domain names.

Related to #549 (Github Pull Request)

Fixes #502 (Github Issue)

Fixes #545 (Github Issue).

Related to #529 (Github Issue).

because the tty port will change

Using the older one likely leads to issues like #517.

added docs, added seperate service for database, pr comments

This flag is necessary for Ansible to ask for the sudo password when using the non-root option as documented in the `hosts` file. Otherwise, Ansible errors out with `missing sudo password`.

Adjust params

This can be removed once turt2live/matrix-dimension#345 is resolved.

Fixes the example, to add the missing required configuration key
for the HTTP policy provider.

Related to #477 (Github Issue).

Related to #454 (Github Pull Request).