[Java SDK] Support contextual tuples for assertions

[jimmyjames]

Checklist

• [X] I agree to the terms within the OpenFGA Code of Conduct.

Describe the problem you'd like to have solved

The Java SDK should support specifying contextual tuples when writing assertions

Describe the ideal solution

The Java SDK is updated to support contextual tuples when writing assertions

Alternatives and current workarounds

No response

References

No response

Additional context

No response