typescript eslint rules should only target typescript files

[noahnu]

Parsing error: ESLint was configured to run on `<tsconfigRootDir>/gatsby/.eslintrc.js` using `parserOptions.project`: <tsconfigRootDir>/tsconfig.json
However, that TSConfig does not include this file. Either:
- Change ESLint's list of included files to not include this file
- Change that TSConfig to include this file
- Create a new TSConfig that includes this file and include it in your parserOptions.project
See the typescript-eslint docs for more info: https://typescript-eslint.io/linting/troubleshooting#i-get-errors-telling-me-eslint-was-configured-to-run--however-that-tsconfig-does-not--none-of-those-tsconfigs-include-this-file

If we only target TS/TSX/MTS/CTS files, I believe we wouldn't have to include the eslintrc file in our tsconfig.json