[proof of concept] different docs reorganization layouts

[Eric-Arellano]

Proposal 1: three-top level entries

https://qiskit-docs-preview-pr-1294.1799mxdls7qz.us-south.codeengine.appdomain.cloud/proposal1

Proposal 2: use section labels

https://qiskit-docs-preview-pr-1294.1799mxdls7qz.us-south.codeengine.appdomain.cloud/proposal2

Proposal 3: workflow index is in dedicated pages - flat design

https://qiskit-docs-preview-pr-1294.1799mxdls7qz.us-south.codeengine.appdomain.cloud/proposal3

Proposal 4: proposal 3 but with labels

https://qiskit-docs-preview-pr-1294.1799mxdls7qz.us-south.codeengine.appdomain.cloud/proposal4