Switch to using an external Ntfy role

The newly extracted role also has native Traefik support,
so we no longer need to rely on `matrix-nginx-proxy` for
reverse-proxying to Ntfy.

The new role uses port `80` inside the container (not `8080`, like
before), because that's the default assumption of the officially
published container image. Using a custom port (like `8080`), means the
default healthcheck command (which hardcodes port `80`) doesn't work.
Instead of fiddling to override the healthcheck command, we've decided
to stick to the default port instead. This only affects the
inside-the-container port, not any external ports.

The new role also supports adding the network ranges of the container's
multiple additional networks as "exempt hosts". Previously, only one
network's address range was added to "exempt hosts".

CHANGELOG.md

@@ -1,3 +1,14 @@
+# 2023-02-17
+
+## The matrix-ntfy role lives independently now
+
+**TLDR**: the `matrix-ntfy` role is now included from another repository. Some variables have been renamed. All functionality remains intact.
+
+The `matrix-ntfy` role (which configures [Ntfy](https://ntfy.sh/)) has been extracted from the playbook and now lives in its [own repository](https://gitlab.com/etke.cc/roles/ntfy). This makes it possible to easily use it in other Ansible playbooks.
+
+You need to **update you roles** (`just roles` or `make roles`) regardless of whether you're enabling Ntfy or not. If you're making use of Ntfy via this playbook, you will need to update variable references in your `vars.yml` file (`matrix_ntfy_` -> `ntfy_`).
+
+
 # 2023-02-15
 
 ## The matrix-grafana role lives independently now