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