initial flex import scripts

Only implements the extratags style for the moment. Tests pass
for the same behaviour as the gazetteer output. Updates still need
to be done.

test/bdd/steps/steps_osm_data.py

@@ -18,6 +18,7 @@ def get_osm2pgsql_options(nominatim_env, fname, append):
                 osm2pgsql=str(nominatim_env.build_dir / 'osm2pgsql' / 'osm2pgsql'),
                 osm2pgsql_cache=50,
                 osm2pgsql_style=str(nominatim_env.get_test_config().get_import_style_file()),
+                osm2pgsql_style_path=nominatim_env.get_test_config().config_dir,
                 threads=1,
                 dsn=nominatim_env.get_libpq_dsn(),
                 flatnode_file='',