feature_service: added cluster feature for system.topology schema change

This patch adds a feature serive which protects the system.topology
schema change against situations where clusters are incompletely
upgraded to new a version and could be rolled back.

gms/feature_service.hh

@@ -116,6 +116,7 @@ public:
     gms::feature collection_indexing { *this, "COLLECTION_INDEXING"sv };
     gms::feature large_collection_detection { *this, "LARGE_COLLECTION_DETECTION"sv };
     gms::feature range_tombstone_and_dead_rows_detection { *this, "RANGE_TOMBSTONE_AND_DEAD_ROWS_DETECTION"sv };
+    gms::feature truncate_as_topology_operation { *this, "TRUNCATE_AS_TOPOLOGY_OPERATION"sv };
     gms::feature secondary_indexes_on_static_columns { *this, "SECONDARY_INDEXES_ON_STATIC_COLUMNS"sv };
     gms::feature tablets { *this, "TABLETS"sv };
     gms::feature uuid_sstable_identifiers { *this, "UUID_SSTABLE_IDENTIFIERS"sv };