Add example of using Expr::field in `37.1.0`

[alamb]

I don't intend to merge this, but I want to put it up to illustrate how to use the 37.1.0 API to do this reasonably

Which issue does this PR close?

Part of https://github.com/apache/datafusion/issues/10181

Rationale for this change

Some users create expressions outside the context of a query that has an analyzer, etc. Some expressions now can only be used via udfs.

What changes are included in this PR?

Add example of using Expr::field in 37.1.0

Are these changes tested?

Are there any user-facing changes?