Run our test case yaml autoformatter in pre-commit

[pokey]

See https://www.cursorless.org/docs/contributing/test-case-recorder/#autoformatting. We would proceed as follows:

• Turn the script into an npm script
• Add support for passing a list of files (as specified in https://pre-commit.com/#arguments-pattern-in-hooks)
• Add a local pre-commit hook with language: node

[auscompgeek]

Done in #1423.