[EPIC] Case Studies to About Section

[csantanapr]

This will replace the "Case Studies" Navigation Menu with "About"

Clicking About goes to an overview "About Knative" Page
Create an About Knative section – add a page that includes diagrams, architecture, high level info about Knative Serving + Eventing similar to Istio: https://istio.io/latest/about/service-mesh/

Section layout for "About" menu:

• About Knative
• Testimonials
• FAQ
• Case Studies
  • deepc
  • outfit7
  • puppet
  • NYT (future)
  • Optum (future)

Sub issues:

• Add "Testimonials" page to knative.dev website #4667
• Add "FAQ" to the knative.dev website #4668
• Add an "About Knative" page #4791

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[abrennan89]

We have a separate epic that the about Knative issue is now part of. Closing this one.