Add initial role for Dendrite as alternative Matrix server

roles/matrix-dendrite/tasks/validate_config.yml

@@ -0,0 +1,16 @@
+---
+- name: Fail if required Dendrite settings not defined
+  fail:
+    msg: >-
+      You need to define a required configuration setting (`{{ item }}`) for using Dendrite.
+  when: "vars[item] == ''"
+  with_items:
+    - "matrix_dendrite_macaroon_secret_key"
+
+- name: (Deprecation) Catch and report renamed settings
+  fail:
+    msg: >-
+      Your configuration contains a variable, which now has a different name.
+      Please change your configuration to rename the variable (`{{ item.old }}` -> `{{ item.new }}`).
+  when: "item.old in vars"
+  with_items: []