[WIP] [SRVKS-969, SRVKS-968] Restructuring Knative serving section

[abrennan89]

Version(s): Applies for OCP 4.8+

Issue: https://issues.redhat.com/browse/SRVKS-969 https://issues.redhat.com/browse/SRVKS-968

Link to docs preview:

• https://51294--docspreview.netlify.app/openshift-enterprise/latest/serverless/serving/knative-services-overview.html
• https://51294--docspreview.netlify.app/openshift-enterprise/latest/serverless/serving/creating-knative-services.html

QE review:

• [ ] QE has approved this change.

[ocpdocs-previewbot]

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Build log: https://circleci.com/gh/ocpdocs-previewbot/openshift-docs/1357