Add .buckconfig to INI filenames

[spenserblack]

Description

This file uses the INI format (source)

Checklist:

• I am adding a new extension filename 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%2F%28%5E%7C%5C%2F%29%5C.buckconfig%2F+root
  • 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/.buckconfig
    • Sample license(s):
      • https://github.com/bluesky-social/social-app/blob/3bab7f7540273a50501780b2f92076fbe41c8022/LICENSE
  • I have included a change to the heuristics to distinguish my language from others using the same extension.