Add clean script

[gn-lluis-u]

🎩 What is the goal?

Allow cleaning the build artifacts. Also allow running clean script in Yarn workspaces that include this package.

📄 How is it being implemented?

Just a call to rm -rf passing the list of postinstall artifacts explicitly excluded from the repository in the .gitignore. file.

✅ How can it be tested?

1. Install this package.
2. Ensure yarn postinstall has been executed
3. Notice the contents of src folder
4. Run yarn clean
5. Notice the contents of src folder, there will be fewer files. Also notice that git status will tell you there are no changes