✨(backend) Index deleted documents

Add SEARCH_INDEXER_COUNTDOWN as configurable setting.
Make the search backend creation simplier (only 'get_document_indexer' now).
Allow indexation of deleted documents.

Signed-off-by: Fabre Florian <ffabre@hybird.org>

src/backend/impress/settings.py

@@ -111,6 +111,9 @@ class Base(Configuration):
     SEARCH_INDEXER_URL = values.Value(
         default=None, environ_name="SEARCH_INDEXER_URL", environ_prefix=None
     )
+    SEARCH_INDEXER_COUNTDOWN = values.IntegerValue(
+        default=1, environ_name="SEARCH_INDEXER_COUNTDOWN", environ_prefix=None
+    )
     SEARCH_INDEXER_SECRET = values.Value(
         default=None, environ_name="SEARCH_INDEXER_SECRET", environ_prefix=None
     )