docs(get-started) Simplify Get Started landing page

[maggiehays]

The main function of this page is to be a landing spot after clicking "Get Started" on the docs home page:

From there, we want end-users to be routed to appropriate resources based on their deployment method.

Checklist

• [ ] The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• [ ] Links to related issues (if applicable)
• [ ] Tests for the changes have been added/updated (if applicable)
• [ ] Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• [ ] For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub