Enable performance tests for sources

[grantr]

Problem
From a performance testing perspective, sources are like channels without a standard ingress. Each source will likely need a custom event generator, but the receiver and everything downstream (aggregator, Mako setup) can be the same as for brokers and channels.

Persona:
Contributor

Exit Criteria
A source has a perf test that shares code with the broker and channel perf tests.

Time Estimate (optional):

Additional context (optional)

/area performance
/project perf/measurement To do
/milestone v0.10.0

[grac3gao-zz]

/assign @grac3gao

[grantr]

/unassign

[chizhg]

Can you be more specific about this requirement? Like which source do we want to test, and which metrics do we want to measure from it?

[grantr]

The title and requirement of this issue is vague, sorry about that. In concrete terms, we want to plug in load generators for any source so that its output can be measured by the generic performance testing tools. I think this was fixed by #1979, and knative/eventing-contrib#669 is an example of how to use it (for KafkaSource).