[chore] complete and normalize the attributes of engine objects (#6258)

Drop outdated engine attributes: supported_languages, language_aliases

Complete, normalize and document the type definitions for the engine-module and
engine-class.

For the ``engine.about`` section of the configuration, a type check is performed
based on structure ``searx.enginelib.EngineAbout``.

The property ``engine.about.language`` no longer exists; existing values have
been migrated to ``engine.language``.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/engines/elasticsearch.py

@@ -55,7 +55,7 @@ about = {
     'official_api_documentation': 'https://www.elastic.co/guide/en/elasticsearch/reference/current/search-search.html',
     'use_official_api': True,
     'require_api_key': False,
-    'format': 'JSON',
+    "results": "JSON",
 }
 
 base_url = 'http://localhost:9200'