Create a "playground" repo where maintainers have admin permissions to test things out

[trask]

Now that we are removing admin permissions from maintainers, a problem arises that maintainers don't have a way to check what settings are available to them within the open-telemetry org (which is sometimes different from what's available in their personal repos).

@reyang suggested (and I like the idea) of creating a "playground" repo where we can give all maintainers admin permissions and they can look at all the settings, and even probably it would be ok for maintainers to update settings and test things out (we could occasionally reset the repo from scratch if that helps).

Are there any concerns with this, or any alternate suggestions?