Add databricks direct unload file containing complex map key

[njaremko]

Required for 7769

[alamb]

Thank you @njaremko 🙏

Could you please add some comments about what this file contains and how you created it?

Ideally you could follow the model of https://github.com/apache/parquet-testing/blob/master/data/README.md

Also I noticed the file is 8KB -- given how widely this repo is cloned / copied is there any way to make the example file smaller?

[njaremko]

I've removed the unneeded columns, and it's 2kb now. I've also updated the readme

[njaremko]

What are the next steps to get this merged?