Add minimal api example for C#

[benjaminsampica]

Description

This blog post gets a ton of organic traffic and a few questions so I figured I’d put it up as an example on the site, too.

Corresponding issue:

Testing

Please explain how you tested this change manually, and, if applicable, what new tests you added. If
you're making a change to just the website, you can omit this section.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded