schema_tables: Load/save extensions table 
schema_tables: Load/save extensions table 

Parses the extension map in tables/views using the registered extension.
If a schema row contains an unknown extension, we just preserve the data
in a placeholder.
avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,scylladb/scylla