Update Knative to 0.7

Description

Knative 0.7 is now available. We should update our serverless / Knative charts.

Istio

We need to understand what changes has been made to Istio deployment, and how it was decoupled from Knative.

Release page: https://github.com/knative/serving/releases/tag/v0.7.0

/cc @DylanGriffith @sebgoa