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/websites.yaml

@@ -5,7 +5,8 @@ websites-defaults: &websites_defaults
   group: Websites
   interval: 1m
   alerts:
-    - type: matrix
+    # - type: matrix
+    - type: custom
       failure-threshold: 5
       success-threshold: 2
       minimum-reminder-interval: "6h"
@@ -15,7 +16,8 @@ websites-staging-defaults: &websites_staging_defaults
   group: Websites (Staging)
   interval: 5m
   alerts:
-    - type: matrix
+    # - type: matrix
+    - type: custom
       failure-threshold: 3
       success-threshold: 1
       minimum-reminder-interval: "24h"
@@ -25,7 +27,8 @@ websites-redirects-defaults: &websites_redirects_defaults
   group: Websites (Redirects)
   interval: 5m
   alerts:
-    - type: matrix
+    # - type: matrix
+    - type: custom
       failure-threshold: 3
       success-threshold: 1
       minimum-reminder-interval: "24h"