Create spec for machine readable json output for "dotnet list package"

[erdembayar]

Sub issue of #7752, json output spec only.

Many organizations are required by regulation to audit packages that they're using in a repository.

Currently there's no easy way to produce a Software Bill of Material (SBOM) output which can be consumed by another auditing system or kept for records.
To do:

• Rename spec md file to DotnetListPackageMachineReadableJsonOutput.md