Provide a friendlier migration message from people using matrix_mxisd_ variables

roles/matrix-ma1sd/tasks/validate_config.yml

@@ -46,7 +46,6 @@
   with_items:
     - "matrix_ma1sd_threepid_medium_email_connectors_smtp_host"
 
-
 - name: (Deprecation) Catch and report renamed ma1sd variables
   fail:
     msg: >-
@@ -55,4 +54,13 @@
   when: "vars | dict2items | selectattr('key', 'match', item.old) | list | items2dict"
   with_items:
     - {'old': 'matrix_ma1sd_container_expose_port', 'new': '<superseded by matrix_ma1sd_container_http_host_bind_port>'}
+
+- name: (Deprecation) Catch and report mxisd variables
+  fail:
+    msg: >-
+      mxisd is deprecated and has been replaced with ma1sd (https://github.com/ma1uta/ma1sd), a compatible fork.
+      The playbook will migrate your existing mxisd configuration and data automatically, but you need to adjust variable names.
+      Please change your configuration (vars.yml) to rename all mxisd variables (`{{ item.old }}` -> `{{ item.new }}`).
+  when: "vars | dict2items | selectattr('key', 'match', item.old) | list | items2dict"
+  with_items:
     - {'old': 'matrix_mxisd_.*', 'new': 'matrix_ma1sd_.*'}