docs: change API route example file extension to .ts and add JS example with switcher prop

[wo-o29]

For Maintainers

What?

Changed the API route example in the documentation to use .ts file extension for the TypeScript example since it uses TypeScript types.
Added a JavaScript example with .js extension using the switcher prop to provide both TypeScript and JavaScript variants in the docs.

Why?

The existing example used a .js extension but included TypeScript-specific type annotations which is inconsistent and could confuse users.
Providing both TypeScript and JavaScript examples improves clarity and usability, catering to a broader audience.

How?

• Updated the filename in the TypeScript example code block to pages/api/hello.ts.
• Added a parallel JavaScript example code block with pages/api/hello.js using the switcher property.
• Ensured both examples show equivalent handler logic with and without type annotations.

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 3498e34

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[phottoo]

looks good!