This new role also adds native Traefik support and support for other
(non-`amd64`) architectures via self-building.

Config was accidently changed when importing upstream changes.

We don't need these 2 roughly-the-same settings related to the
traefik-certs-dumper role.

For Traefik, it makes sense, because it's a component used by the
various related playbooks and they could step onto each other's toes
if the role is enabled, but Traefik is disabled (in that case, uninstall
tasks will run).

As for Traefik certs dumper, the other related playbooks don't have it,
so there's no conflict. Even if they used it, each one would use its own
instance (different `devture_traefik_certs_dumper_identifier`), so there
wouldn't be a conflict and uninstall tasks can run without any danger.

This helps people who run federation on another domain (etc.).
They should now easily be able to add a custom rule for federation traffic.

Fixes a regression introduced in 0220c851e8

BuildX is required for building this container image.

This makes it consistent with the rest of the playbook:
- there's a default config which has various variables controlling
  settings
- there's also an `_extension_yaml` variable, which lets you override it

We disable it via `group_vars/matrix_servers`, as we do for all other
roles.

The next task asks for a daemon reload, so there's no need to do it
twice.

Larger deployments may wish to run migration more often.

`always` is an nginx suffix, which shouldn't have been added to these.