feat(alertmanager_receiver): add role

roles/alertmanager_receiver/README.md

@@ -0,0 +1,17 @@
+# `finallycoffee.matrix.alertmanager_receiver` ansible role
+
+This ansible role deploys and configures
+[`matrix-alertmanager-receiver`](https://github.com/metio/matrix-alertmanager-receiver),
+a fork of [https://git.sr.ht/~fnux/matrix-alertmanager-receiver] with more features.
+For futher information, see [the project's `README`](https://github.com/metio/matrix-alertmanager-receiver?tab=readme-ov-file#matrix-alertmanager-receiver-).
+
+## Configuration
+
+### Required configuration
+
+The following variables *must* be populated or else the role will be unable to
+set up the service successfully:
+
+- `alertmanager_receiver_config_matrix_homeserver_url` - matrix homeserver URL
+- `alertmanager_receiver_config_matrix_user_id` - full userid (`@user:instance.tld`)
+- `alertmanager_receiver_config_matrix_access_token` - access token for that user