[ERTP] Basic non-fungible use case in ERTP tests (event tickets)

[katelynsills]

For Zoe Alpha, we need a basic non-fungible use case in the ERTP tests. We can start with the documentation that @DavidBruant wrote for event tickets.

This non-fungible use case would probably use the natListExtentOps or handleExtentOps from the Minimum Extent Ops (#521). If we want to use strings rather than Nats or handles, we could do that, but we will have to spend time implementing the strListExtentOps (#538) as part of Zoe Alpha.

This is a precursor to #543, which is taking this example and putting it in a Zoe contract to deploy to the testnet.

[DavidBruant]

I'm going to go with handleExtentOps because it feels the most relevant to the use case. Also the concept and the code is new, so it'll be a good occasion to exercise it
I'm going to create a branch/PR on top of no-config-add-brand. I'll rebase regularly as this branch changes

[katelynsills]

Closed by #558