[enh] engines: add about variable

move meta information from comment to the about variable
so the preferences, the documentation can show these information

searx/engines/dummy.py

@@ -1,10 +1,18 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
  Dummy
-
- @results     empty array
- @stable      yes
 """
 
+# about
+about = {
+    "website": None,
+    "wikidata_id": None,
+    "official_api_documentation": None,
+    "use_official_api": False,
+    "require_api_key": False,
+    "results": 'empty array',
+}
+
 
 # do search-request
 def request(query, params):