This PR:

• Removes the API quickstarts page and redirects to the Elasticsearch quickstarts page instead.
• Moves the QueryDSL and ES|QL search quickstarts into the get-started folder and removes the word "tutorial" from the filename.
• Moves the Basics quickstart to the Get started section, since it's not applicable only to the Elasticsearch solution.
  • Updates this page to use the stepper component

This PR relates to #1922 (review) ("My instinct is that we should group them together as soon as possible, feels a little hidden in this new section. They're all hands-on guides, just using different interfaces.)