Add changelogs for M.E.AI projects

[stephentoub]

Microsoft Reviewers: Open in CodeFlow

[eiriktsarpalis]

Thanks. Should we be appending entries on a per-change basis or would this get compiled from the git history every time we push a release?

[stephentoub]

Thanks. Should we be appending entries on a per-change basis or would this get compiled from the git history every time we push a release?

I'm fine with either. I did this one by taking 10 minutes and just going through the commits. The repo also has an auto-generated changelog for https://github.com/dotnet/extensions/releases, but that's for the whole repo rather than per library and only for stable releases rather than previews. I spoke with Jose about possibly trying out various alternatives, but in the meantime, we can keep going with these AI-specific, manually-updated ones.