Automate the testing of SQL commands

Jesse Seldess commented:

We have SQL commands throughout almost all of our tutorials and how-tos (e.g., [Learn CockroachDB SQL](https://www.cockroachlabs.com/docs/stable/learn-cockroachdb-sql.html), [SQL Tuning with `EXPLAIN`](https://www.cockroachlabs.com/docs/stable/sql-tuning-with-explain.html), and in examples throughout our SQL reference docs (e.g., [`CREATE INDEX`](https://www.cockroachlabs.com/docs/stable/create-index.html#examples]). Just as with driver/ORM code samples, it'd be ideal to automate the testing of our SQL commands to ensure our docs are accurate and copy/paste-able for users.

Possible actions:
- [ ) Use a consistent dataset (built-in to cockroach) across SQL docs. @ericharmeling and @rmloveland made some initial progress here using the `movr` dataset built into [`cockroach demo`](https://www.cockroachlabs.com/docs/stable/cockroach-demo.html] on a subset of SQL docs. We should verify that's the approach we want.
- [ ) Automate the testing of the code on a regular basis via CI. Approach may be the same or different to https://github.com/cockroachdb/docs/issues/7066.

Jira Issue: DOC-485