feat: add support for TypeScript based configs

[xeho91]

Resolves #631

This PR contains a:

• [ ] bugfix
• [x] new feature
• [ ] code refactor
• [x] test update
• [ ] typo fix
• [ ] metadata update

Motivation / Use-Case

TailwindCSS since version ^3.3.0 has support for TypeScript based configs. Including PostCSS.

Hence, I've added patterns to search for config files, which end with the following extensions:

• cts
• mts
• ts

Breaking Changes

None so far.

Additional Info

631

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: xeho91 / name: Mateusz Kadlubowski (dd2166b716756f83b4d30f7b764411f1e786a75d)

[xeho91]

I had to install two packages:

• cosmiconfig-typescript-loader to load TypeScript configs, apparently by default cosmiconfig doesn't support TypeScript extensions.
• postcss-load-config as devDependency, because I needed the types to add to the config. Using any or unknown would break with the current lint setup.

I have added test cases for two config types:

• postcss.config.ts (ESM)
• postcss.config.cts (CJS)

Lemme know if it's enough. I have skipped the other possible patterns, e.g. postcssrc.ts, etc. Locally the tests for config-autoload/ pass successfully for me; however, the other tests fail- and I have no clue if they're relevant. Any guidance would be much appreciated. :pray:

[alexander-akait]

Oh, there is a bug in npm, I will merge and will fix it in the other PR, thank you for the PR