Include machine-readable info in markdown comment in release announcement post

[lbussell]

We should add some parseable data in a markdown comment in the automated source-build release announcement discussion post, so that distro maintainers can trigger automation when the announcement goes out for new releases. The data should include the git tag to pull from the installer repo, and potentially a github.com URL directly to the tag.

See #1836 (comment)

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[MichaelSimons]

[Triage] We should prioritize this after 7.0 gets to a shippable state. If a customer/maintainer is asking for it, then we should consider bumping the priority.

[lbussell]

@dotnet/distro-maintainers would this be valuable for querying info about releases? What info would be needed? I could easily include things like:

• dotnet/installer release tag/sha
• SDK version
• Runtime version
• Release channel (6.0)

I was thinking of using json inside of a comment in the announcement discussion. Would a different format be better?

[omajid]

For me, those 4 pieces of info would be sufficient.