Actions: Consider splitting "playground" out of production "environment"

[spbnick]

At the moment GitHub Actions only have a notion of "production" environment, which includes both "production" and "playground". The "staging" environment is separate.

However, we only use "staging" for pull request and manual testing, and there's no real data there. OTOH, "playground" has quite a bit of data sent by various people, and it would be good to have the deployment confirmation cut off after it, and not after just "staging", so that we can catch more potential issues before deploying to actual production.

Consider separating "playground" into its own "environment" in terms of GitHub Actions.