Add the Ballerina Central case study

[praneesha]

Purpose

Add the Ballerina Central case study.

Fixes #

Checklist

• Page addition

  • Add permalink to pages.

• Page removal

  • Remove entry from corresponding left nav YAML file.
  • Add redirect_from on the alternative page.
  • If no alternative page, add redirection on the redirections.js file.

• Page rename

  • Add front-matter redirect_from.
  • Add front-matter redirect_to: (if applicable).

• Page restrcuture

  • Add permalink to pages.
  • Add front-matter redirect_from.
  • Add front-matter redirect_to: (if applicable).

[sm1990]

@praneesha Please update the link in https://ballerina.io/#users section