Add .json.example as JSON extension

[spenserblack]

This extension turned out to be far more popular than I expected.

Checklist:

• I am adding a new extension to a language.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.json.example Since this is a data format there aren't really keywords to include in the search. While it seems to be a very popular extension, everyone uses it differently (like .env.example).
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/bluesky-social/social-app/blob/017b7647b18cc67201c5b4e9c5da36a53257daa9/google-services.json.example
    • Sample license(s):
      • https://github.com/bluesky-social/social-app/blob/017b7647b18cc67201c5b4e9c5da36a53257daa9/LICENSE
  • I have included a change to the heuristics to distinguish my language from others using the same extension.