### Description

This PR adds support for the **Kinyarwanda** language.

* Created `kinyarwanda.json` with a word list of 200+ unique, lowercase
words.
* Registered `"kinyarwanda"` in the shared `LanguageSchema` within
`packages/schemas` to ensure type safety across the monorepo.
* Added `"kinyarwanda"` to the `LanguageGroups` in the frontend
constants so it appears correctly in the user settings menu under the
appropriate category.

### Checks

* [x] Adding/modifying Typescript code?
* [x] I have used `qs`, `qsa` or `qsr` instead of JQuery selectors.


* [ ] Adding quotes?
* [x] Adding a language?
* Make sure to follow the [[languages
documentation](https://github.com/monkeytypegame/monkeytype/blob/master/docs/LANGUAGES.md)](https://github.com/monkeytypegame/monkeytype/blob/master/docs/LANGUAGES.md)
* [x] Add language to `packages/schemas/src/languages.ts`
* [x] Add language to exactly one group in
`frontend/src/ts/constants/languages.ts`
* [x] Add language json file to `frontend/static/languages`


* [ ] Adding a theme?
* [ ] Adding a layout?
* [ ] Adding a font?
* [x] Check if any open issues are related to this PR; if so, be sure to
tag them below.
* [x] Make sure the PR title follows the Conventional Commits standard.
* [x] Make sure to include your GitHub username prefixed with @ inside
parentheses at the end of the PR title.