feat(element): add ansible role

roles/element/docs/docker.md

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+# `element` deployment using `docker`
+
+> [!NOTE]
+> Needs the python library `docker` on the `ansible_host`.
+
+## Configuration
+
+The following options to the
+[`docker_container` module](https://docs.ansible.com/ansible/latest/collections/community/docker/docker_container_module.html)
+are available under the `element_container_` prefix:
+
+- `env`
+- `ports`
+- `labels`
+- `networks`
+- `etc_hosts`
+- `purge_networks`
+
+The following variables are pre-populated by the role, so override them with care:
+
+- `name`
+- `image`
+- `user`
+- `volumes`
+- `restart_policy`
+
+## Pulling from a self-hosted container registry
+
+Set `element_container_image_registry` to use a self-hosted docker registry / mirror / cache.
+
+If you need to authenticate to your registry and are not yet logged in, set `element_container_image_registry_{username,password}` and the role will attempt to log in.
+
+Set `element_container_image_registry_reauthorize` to `true` if you want to force a reauthorization at the registry.