Begin movie_rentals (lite) data set

[seancolsen]

This is a smaller version of the movie rentals data set

[seancolsen]

@mathemancer, as discussed during our engineering meeting today, I'd like to try handing this off to you to see if you can help us get this over the finish line for 0.7.0.

Here's how to pick up where I left off:

1. See the new README.md file I've added in this PR.

2. Run the steps listed in the README to generate a SQL file.

3. Notice that this file has psql commands, so it won't fit cleanly into the sample data importing system that we've set up in the application. We need to figure out a way to generate a cleaner version of this file — or potentially just commit it into the app repo with some manual massaging.

In the app repo, I would expect the SQL dump to go into mathesar/examples/resources/. And we'll need to add some supporting code akin to mathesar/examples/library_dataset.py, plus the corresponding front end code in src/systems/databases/create-database/InstallationSchemaSelector.svelte.