Add a JSON representation of platform packages for a release to release-notes

The release notes for specific releases of .NET contain a list of all of the relevant NuGet packages and versions that are associated with it (e.g. [8.0.13's](https://github.com/dotnet/core/blob/main/release-notes/8.0/8.0.13/8.0.13.md#packages-updated-in-this-release)), but this information only appears to be available as Markdown.

It would be advantageous for automated tools to be able to access a JSON representation of this information to avoid the need for manual curation of a list of "what packages are part of the platform" or the need to parse the markdown (example: https://github.com/dependabot/dependabot-core/pull/11127).

As well as some tooling of my own for update automation ([martincostello/dotnet-bumper](https://github.com/martincostello/dotnet-bumper), [martincostello/update-dotnet-sdk](https://github.com/martincostello/update-dotnet-sdk)), other tools such as dependabot and [dotnet-outdated/dotnet-outdated](https://github.com/dotnet-outdated/dotnet-outdated) could access this data to make themselves more intelligent and/or avoid writing their own solutions to determine them.

I assume that the markdown itself is constructed through some sort of automation, so also generating additional JSON shouldn't be much of an additional burden?

/cc @richlander @slang25 @brettfo