Create saved_queries table plus a canned query that writes to it

[simonw]

Plugin idea: datasette-saved-queries - it uses the startup hook to initialize a saved_queries table, then uses the canned_queries hook to add a writable canned query for saving records to that table.

Then it returns any queries from that table as additional canned queries.

Bonus idea: it could write the user's actor_id to a column if they are signed in, and provide a link to see "just my saved queries" in that case.
Originally posted by @simonw in simonw/datasette#852 (comment)

[simonw]

First bit I'm going to implement is the startup hook that creates the tables and the canned query that lets users save a query.