Add QIT workflow

[tomalec]

Changes proposed in this Pull Request:

Add a manual QIT workflow so we can run the tests before the release w/o leaving the GitHub context.

Checks:

• [x] Does your code follow the WordPress coding standards?
• [ ] Have you written new tests for your changes, as applicable?
• [x] Have you successfully run tests with your changes locally?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Screenshots:

Detailed test instructions:

Manual workflows require to be merged to trunk to work, so you can either

1. Fork the repo
2. Merge to trunk
3. Run the workflow or
4. Merge this PR and try :goberserk:

This is a clone of GLA version https://github.com/woocommerce/google-listings-and-ads/pull/2114

Additional details:

Changelog entry

Dev - Add QIT workflow