E2E Test - Tracing through CronJobSource

[Harwayne]

This should not be started until after #1758 is closed.

Problem
In order to ensure that CronJobSource generates traces correctly, we need an E2E test.

Persona:
Contributor

Exit Criteria
A test in the e2e suite that runs before every PR merge. The test verifies that an event sent from a CronJobSource sent to something that doesn't emit traces (e.g. a simple web server) still creates a trace with a span for the communication between CronJobSource and its sink.

[Harwayne]

/project Observability To do

[n3wscott]

similar to https://github.com/knative/eventing/blob/master/test/conformance/broker_tracing_test.go and https://github.com/knative/eventing/blob/master/test/conformance/channel_tracing_test.go.

/good-first-issue

[knative-prow-robot]

@n3wscott:
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In response to this:

similar to https://github.com/knative/eventing/blob/master/test/conformance/broker_tracing_test.go and https://github.com/knative/eventing/blob/master/test/conformance/channel_tracing_test.go.

/good-first-issue

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