Provoked by https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3900

We do not let bridges update config files, so generation cannot happen.
We don't want the bridge to manage the config file anyway.

Media didn't work before this patch, likely because this feature is broken:

> N.B. Discord now requires signed expiring download links, which means this solution no longer works. In the future, a more dynamic solution may be implemented where requests go to the bridge and the bridge and the bridge refetches the message if necessary.

Source: https://docs.mau.fi/bridges/go/discord/direct-media.html

Moreover, most users more likely don't want this behavior and would
prefer to keep a complete mirror of the media on Matrix, instead of
going through two 3rd party servers to fetch the media on demand.

The default config for the bridge
(https://github.com/mautrix/discord/blob/main/example-config.yaml)
actually does not enable it.

It seems like 4ed522e8fe
(https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3133)
lied to us as to what upstream does. Poor PR review lead to this
anti-feature making it into the playbook.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3133

Regression since 4ed522e8fe

Related to https://github.com/mautrix/discord/issues/95

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.

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

Update group_vars/matrix_servers

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

Remove old data migration tasks

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

Update roles/matrix-bridge-mautrix-discord/tasks/validate_config.yml

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

Redo bridge permissions