status(host): use custom alert for Matrix to make it work with PAT

The Personal Access Token we use isn't compatible with the default
Matrix alerting provider, so use a custom alert.

resources/external/status/docker_compose/config/general.yaml

@@ -18,10 +18,21 @@ ui:
   default-sort-by: group
 
 alerting:
-  matrix:
-    server-url: "https://matrix.nekover.se"
-    access-token: "${MATRIX_ACCESS_TOKEN}"
-    internal-room-id: "!jG755onbGAH-lZsZo8SRKtlsncSMvq7nzPhwCi5CgdQ"
+  # matrix:
+  #   server-url: "https://matrix.nekover.se"
+  #   access-token: "${MATRIX_ACCESS_TOKEN}"
+  #   internal-room-id: "!jG755onbGAH-lZsZo8SRKtlsncSMvq7nzPhwCi5CgdQ"
+  custom:
+    url: "https://matrix.nekover.se/_matrix/client/v3/rooms/%21jG755onbGAH-lZsZo8SRKtlsncSMvq7nzPhwCi5CgdQ/send/m.room.message"
+    method: "POST"
+    body: |
+      {
+        "msgtype": "m.text",
+        "body": "[ALERT_TRIGGERED_OR_RESOLVED]: [ENDPOINT_GROUP] - [ENDPOINT_NAME] - [ALERT_DESCRIPTION] - [RESULT_ERRORS]"
+      }
+    headers:
+      Authorization: "Bearer ${MATRIX_ACCESS_TOKEN}"
+
 
 # A bit more than the default 5 concurrent checks should be fine.
 concurrency: 15