[OTel]: create rekt tracing tests

**Problem**
We currently have tracing tests for Zipkin in the conformance test suite. However, they are relatively complex to change.

We should implement new tracing tests into the rekt test suite

**[Persona:](https://github.com/knative/eventing/blob/main/docs/personas.md)**
Which persona is this feature for?

**Exit Criteria**
A measurable (binary) test that would indicate that the problem has been resolved.

**Time Estimate (optional):**
How many developer-days do you think this may take to resolve?
2-3 days

**Additional context (optional)**
Add any other context about the feature request here.

Start by comparing the existing Zipkin tracing tests in the conformance test suite with the rekt test suite. Identify the tracing behavior that must be covered and determine how the new tests can provide binary pass/fail results. Done means the required tracing tests run successfully in rekt and cover the intended behavior.

Written by the indexing model from the issue text.