* Rename variables matrix_bot_postmoogle_* with matrix_postmoogle_*

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Rename file names and references to those files

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Move variables block for /matrix-bridge-postmoogle

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Rename matrix_playbook_bot_postmoogle_ to matrix_playbook_bridge_postmoogle_

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Add matrix_playbook_migration_matrix_postmoogle_migration_validation_enabled

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Replace an install tag example with "-bot" prefix

The previous example seems to have been selected to show how components whose name contains "-bot-" needed to be specified.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

---------

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>
Co-authored-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

- forego removing Docker images - it's not effective anyway, because it
  only removes the last version.. which is a drop in the bucket, usually

- do not reload systemd - it's none of our business. `--tags=start`,
  etc., handle this

- combine all uninstall tasks under a single block, which only runs if
  we detect traces (a leftover systemd .service file) of the component.
  If no such .service is detected, we skip them all. This may lead to
  incorect cleanup in rare cases, but is good enough for the most part.

This paves the way for installing other roles into `roles/galaxy` using `ansible-galaxy`,
similar to how it's done in:

- https://github.com/spantaleev/gitea-docker-ansible-deploy
- https://github.com/spantaleev/nextcloud-docker-ansible-deploy

In the near future, we'll be removing a lot of the shared role code from here
and using upstream roles for it. Some of the core `matrix-*` roles have
already been extracted out into other reusable roles:

- https://github.com/devture/com.devture.ansible.role.postgres
- https://github.com/devture/com.devture.ansible.role.systemd_docker_base
- https://github.com/devture/com.devture.ansible.role.timesync
- https://github.com/devture/com.devture.ansible.role.vars_preserver
- https://github.com/devture/com.devture.ansible.role.playbook_runtime_messages
- https://github.com/devture/com.devture.ansible.role.playbook_help

We just need to migrate to those.

Signed-off-by: Sebastian Gumprich <github@gumpri.ch>