NotImplemented: serializing ExampleFunctionOptionsType to StructScalar

when running example compute_register_example, it report an exception:

NotImplemented: serializing ExampleFunctionOptionsType to StructScalar

**Reporter**: [darion yaphet](https://issues.apache.org/jira/browse/ARROW-15443) / @darionyaphet

_{**Note**: *This issue was originally created as [ARROW-15443](https://issues.apache.org/jira/browse/ARROW-15443). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Start by running the compute_register_example entry point to reproduce the NotImplemented exception, then trace the serialization path for ExampleFunctionOptionsType to StructScalar. Done means the example no longer reports this exception and the serialization behavior is covered by an appropriate test.

Written by the indexing model from the issue text.