Add a sample that uses a workflow to lock resources

[nagl-temporal]

What was changed

Adds a new sample that demonstrates how to use a workflow to mediate access to a small pool of resources.

Why?

A customer asked for an example of how to do this kind of thing. We ruled out worker-specific task queues and sessions - those work best when you can run the worker in/near the protected resource. They cannot, for security reasons, which leaves us with:

• non-temporal approaches to resource locking, or
• something like this

Checklist

1. How was this tested:
   Ran the worker and starter per the readme.

2. Any docs updates needed?
   No - it's just a sample.

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[cretz]

There is a pattern for doing this with signal-with-start. You can see a sample in .NET, Go, and TypeScript.

Would totally support such a sample in Python. Needs to be a simple Lock class usable in a workflow with similar semantics to https://docs.python.org/3/library/asyncio-sync.html#asyncio.Lock but does signal with start and such. Also make sure we have a test or two. Feel free to adapt this PR (or close it and I can make an issue tracking that we need such a sample).