add matrix_continuwuity_url_preview_domain_contains_allowlist variable

roles/custom/matrix-continuwuity/defaults/main.yml

@@ -196,3 +196,6 @@ matrix_continuwuity_environment_variables_extension: ''
 
 matrix_continuwuity_forbidden_remote_server_names: []
 matrix_continuwuity_forbidden_remote_room_directory_server_names: []
+
+# Controls the `url_preview_domain_contains_allowlist` setting.
+matrix_continuwuity_url_preview_domain_contains_allowlist: []

roles/custom/matrix-continuwuity/templates/continuwuity.toml.j2

@@ -1215,7 +1215,7 @@ forbidden_remote_room_directory_server_names = {{ matrix_continuwuity_forbidden_
 # attack surface to your server, you are expected to be aware of the risks
 # by doing so.
 #
-#url_preview_domain_contains_allowlist = []
+url_preview_domain_contains_allowlist = {{ matrix_continuwuity_url_preview_domain_contains_allowlist | to_json }}
 
 # Vector list of explicit domains allowed to send requests to for URL
 # previews.