Add GitHub Action that adds context-v2 label everywhere

[dcastil]

I'm putting the context-v2 label on every new issue, discussion and PR manually to mark it as having been created in the context of tailwind-merge v2. Would be nice to build a GitHub action that does this automatically whenever a new issue, discussion or PR is created in this repository.

Here are the docs for GitHub Actions: https://docs.github.com/en/actions
And here is the workflow syntax explained: https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions

If anyone wants to pick it up, I'm accepting PRs for this and also happy to help if needed. 😊

[github-actions]

This was addressed in release v2.4.0.