Fix documentation (quickstart, samples) for changes to install

[kalantar]

Is your feature request related to a problem? Please describe.
Issue https://github.com/iter8-tools/iter8-install/issues/50 updates install. Need to make sure all quickstart and samples work.

Why is the feature useful for Iter8 users?
Basic function

Describe the solution you'd like
Update as needed.

Describe alternatives you've considered
None

Does this issue require a design doc/discussion? If there is a link to the design document/discussions, please provide it below.

• Update knative quickstart to call out install of metrics/Prometheus
• Update all knative tutorials to indicate need for metrics (and Prometheus)
• Update knative canary progressive tutorial to explicitly add rbac rules for helm (they are removed from default install)

How will this feature be tested?
[ ] TBD

How will this feature be documented?
This is documentation.