feat(mongodb-runner): add mongodb-runner ls --json

[addaleax]

Provide JSON-formatted output that contains serialized cluster data.

Description

Open Questions

Checklist

• I have signed the Contributor License Agreement (https://www.mongodb.com/legal/contributor-agreement)
• New tests and/or benchmarks are included
• Documentation is changed or added

[nbbeeken]

tried it out locally, lgtm! just a thought:

[nbbeeken]

    .option('verbose', { type: 'boolean', describe: 'Enable verbose output' })
    .command('start', 'Start a MongoDB instance')
    .command('stop', 'Stop a MongoDB instance')
    .command('prune', 'Clean up metadata for any dead MongoDB instances')
    .command('ls', 'List currently running MongoDB instances', (yargs) => {
      return yargs.option('json', {
        type: 'boolean',
        describe: 'Output machine-readable JSON',
      });
    })

just a suggestion, you could nest it under ls, it's still top-level on argv so no code change below needed.