Dynamic DNS

Related to #681 (Github Pull Request)

Related to #681 (Github Pull Request)

We'd like the roles to be self-contained (as much as possible).

Thus, the `matrix-nginx-proxy` shouldn't reference any variables from
other roles. Instead, we rely on injection via
`group_vars/matrix_servers`.

Related to #681 (Github Pull Request)

If `matrix_dynamic_dns_enabled`, we'd like to ensure there's at least
one configuration defined.

Related to #681 (Github Pull Request)

- `item` was undefined
- `'key' in configurations == ''` was doing the wrong thing

Related to #681 (Github Pull Request)

Having it unset in the role itself (while referencign it) is a little strange.

Now people can look at the `roles/matrix-dynamic-dns/defaults/main.yml`
file and figure out everything that's necessary to run the role.

Related to #681 (Github Pull Request)

Related to #681 (Github Pull Request)

Upgrade Element (1.7.12 -> 1.7.13)

Added docker-compose example for launching Traefik.

This broke in 63a49bb2dc.

Proxying the OpenID Connect endpoints is now possible,
but needs to be enabled explicitly now.

Supersedes #702 (Github Pull Request).

This patch builds up on the idea from that Pull Request,
but does things in a cleaner way.

Switch to the new vectorim/element-web Docker image

This reverts commit 7d211b71e2.

The multi-arch images are now available, as discussed in #699 (Github Issue).

Fixes #696 (Github Issue)

We do this to match Synapse's new default "max_upload_size" (50MB).

This `matrix_nginx_proxy_proxy_matrix_client_api_client_max_body_size_mb`
default value only affects standalone usage of the `matrix-nginx-proxy`
role. When the role is used in the context of the playbook,
the value is dynamically assigned from `group_vars/matrix_servers`.

Somewhat related to #692 (Github Issue).

The regex introduced in 63a49bb2dc seems to take precedence
over the bare location blocks, causing a regression.

> It is important to understand that, by default, Nginx will serve regular expression matches in preference to prefix matches.
> However, it evaluates prefix locations first, allowing for the administer to override this tendency by specifying locations using the = and ^~ modifiers.

Source: https://www.digitalocean.com/community/tutorials/understanding-nginx-server-and-location-block-selection-algorithms

Regression since 63a49bb2dc.

Related to #685 (Github Issue).

We now automatically expose the APIs when Synapse Admin is enabled.

While v1.22.0 supposedly has multi-arch Docker images
(thanks to https://github.com/matrix-org/synapse/pull/7921),
I can't them on Docker Hub yet, so I'm backing out of this change
for now and letting people fall back to self-building there.

Fix docker mount instruction in documentation

Fixes #685 (Github Issue).

The SSL certificates should be accessible to the nginx proxy container, not the synapse container.