Determine default target for broker ingress events per second

[grantr]

Problem
What is our default target for published events per second handled by the broker ingress service? This is separate from the fanout's delivered events per second (and is likely to be lower).

Persona:
User

Exit Criteria
We have a goal in published events per second to tune the default ingress resource requirements.

Part of #1552.

[grantr]

@liu-cong suggests default target 1000 events per second.

[yolocs]

The default target I'm setting for a single ingress pod is: <= 1000 qps, <= 256k event size.