feat(alternator): adding the getting-started sample page

[DanielHe4rt]

Changelog

Adding ScyllaDB Alternator examples and new section focused on the subject.

Changes

• [x] Added: Alternator 'Getting Started' Page
• [x] Added: Alternator 'Design and Data Model' Page
• [x] Examples: Alternator + PHP
  • [x] Step by step Doc
  • [x] Sample Project
• [x] Examples: Alternator + Python
  • [x] Step by step Doc
  • [x] Sample Project
• [ ] Examples: Alternator + JS
  • [ ] Step by step Doc
  • [ ] Sample Project