Define custom lint rule to assert that each CLI command lists examples

[andrewjensen]

This defines a custom ESLint rule called require-cli-examples, to assert that each "leaf node" command includes examples in its help output.

This means that any command that has an action() must also call:

.addHelpText(
  "afterAll",
  createExampleText([ /* ... */ ])

This rule helps us guarantee good UX for users that need more information about a command.

The rule caught missing examples in the following commands, so this PR also defines examples for them:

• dx auth login
• dx auth logout
• dx auth status
• dx init

[andrewjensen]

ESLint has its own little test helper with RuleTester, so this is basically just a shim to connect it with our main vitest suite.

See the custom rule tutorial: Step 6: write the test

[emmahoggan]

Love this - pits of success 🔥