[component] Harvest

As a Workflow Developer,
I want to be able to use the native **Harvest** connector,
So that I can implement more complex integration use cases involving **Harvest**.

**References**

- Website: https://www.getharvest.com/

- Documentation: https://help.getharvest.com/api-v2/

**Acceptance Criteria**

Implemented actions:

- [ ] get invoice

TODO

Implemented triggers
TODO

Definition of Done:

**Definition of Done**

- [ ] Unit/Integration tests
- [ ] Connection setup steps
- [ ] Guidejar tutorial for connection setup
- [ ] Documentation is generated and available

Start with the Harvest API v2 documentation and inspect existing connector patterns in the repository. Implement the listed get-invoice action, clarify the trigger scope, and cover the connection setup, unit/integration tests, Guidejar tutorial, and generated documentation described in the Definition of Done.

Written by the indexing model from the issue text.