[Task]: Version-control all generated Playground files

[alexeyinkin]

What needs to happen?

1. Version-control all generated files.
2. Exclude all generated files from Apache Rat check (this really is the most painful thing with their version-controlling as we had been adding licenses manually there).
3. When building a Docker container, delete and re-generate all generated files so that their manual modifications have no effect in deployment and we see errors stemming from that early.
4. Add a Gradle task to delete all generated files so that generation is easy to verify and we can test the generated files' consistency before deployment.
5. Delete and re-generate all generated files in :playground:frontend:precommit
6. Add a GitHub post-commit workflow to re-generate files and to compare them with the committed versions. Break if a difference is found. This way the committer will receive an email and will soon make it a habit to run the local pre-commit task.

Issue Priority

Priority: 3

Issue Component

Component: beam-playground

[alexeyinkin]

.remove-labels 'awaiting triage'

[alexeyinkin]

.take-issue