split up table creation SQL into separate files

lib-sql/tables/importance_tables.sql

@@ -0,0 +1,16 @@
+-- SPDX-License-Identifier: GPL-2.0-only
+--
+-- This file is part of Nominatim. (https://nominatim.org)
+--
+-- Copyright (C) 2026 by the Nominatim developer community.
+-- For a full list of authors see the git log.
+
+{% if 'wikimedia_importance' not in db.tables and 'wikipedia_article' not in db.tables %}
+-- create dummy tables here if nothing was imported
+CREATE TABLE wikimedia_importance (
+  language TEXT NOT NULL,
+  title TEXT NOT NULL,
+  importance double precision NOT NULL,
+  wikidata TEXT
+)  {{db.tablespace.address_data}};
+{% endif %}