Issues and Pull Requests were not migrated to the new
organization/repository, so `matrix-org/synapse/pull` and
`matrix-org/synapse/issues` references were kept as-is.

`matrix-org/synapse-s3-storage-provider` references were also kept,
as that module still continues living under the `matrix-org` organization.

This patch mainly aims to change documentation-related things, not actual
usage in full yet. For polish that, another more comprehensive patch is coming later.

We'd be adding integration with an internal Traefik entrypoint
(`matrix_playbook_internal_matrix_client_api_traefik_entrypoint`),
so renaming helps disambiguate things.

There's no need for deperecation tasks, because the old names
have only been part of this `bye-bye-nginx-proxy` branch and not used by
anyone publicly.

This also adds labels for Synapse. Support for other homeservers and
components will be added later.

This also updates validation tasks and documentation, pointing to
variables in the matrix-synapse role which don't currently exist yet
(e.g. `matrix_synapse_container_labels_client_synapse_admin_api_enabled`).

These variables will be added soon, as Traefik labels are added to the
`matrix-synapse` role. At that point, the `matrix-synapse-reverse-proxy-companion` role
will be updated to also use them.

the old one is deprecated (says the page at the link target), and refers to this new one.

* Add example configuration for Caddy v2

Add a basic example how to get synapse-admin running behind Caddy v2 proxy.

* Improve working, fix typos

* Fix typos

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

Related to https://github.com/Awesome-Technologies/synapse-admin/issues/132

Regression since 63a49bb2dc.

Related to #685 (Github Issue).

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

Fixes #562 (Github Issue)