Use the new Workgen API when creating tables in the sample workload

In WT-10238, we added a new Workgen API to let Workgen know a new table is available to be worked on. This API was called create_table and might be later renamed in WT-10239 as add_table.

This new API should be called during the run phase every time a new table is created. See the create function in example_dynamic_tables.py as an example where workload.add_table(table_name) is called.