As somebody interested in using Greenhouse I would like to have a step-by-step getting started guide, so that I can easily deploy my own setup

The current Quick start guide is targeted towards onboarding new organisations but not towards deploying Greenhouse.

As part of the first release there should be documentation on how to deploy greenhouse into a local environment.
The current steps on how to setup the SAP IAS should be replaced with at least one open-source alternative

Acceptance Criteria

• The Quick start guide covers how to deploy Greenhouse into the local environment a Gardener Shoot cluster
• Changes/Documentation of the Helm Chart to make it easily consumable
• The Sign up section is kept but adapted towards another IAS provider