Ability to get assistance for a specific table

[simonw]

There's a menu item for this already but it doesn't work yet:

https://github.com/datasette/datasette-query-assistant/blob/cb71eae6cf7ff248033940c88dccc1c9e1a68d01/datasette_query_assistant/__init__.py#L135-L150

It should send just the schema for the table and any tables related to it by foreign key.