docs(OpenTelemetry): add example project

[evansims]

Please do not report security vulnerabilities here. See the Responsible Disclosure Program.

Thank you in advance for helping us to improve this library! Please read through the template below and answer all relevant questions. Your additional work here is greatly appreciated and will help us respond as quickly as possible.

By submitting an issue to this repository, you agree to the terms within the OpenFGA Code of Conduct.

Describe the problem you'd like to have solved

As we do for the other SDKs, we should add an example project for using the Java SDK with OpenTelemetry.

Describe the ideal solution

N/A

Alternatives and current workarounds

A clear and concise description of any alternatives you've considered or any workarounds that are currently in place.

Additional context

Add any other context or screenshots about the feature request here.