Consider publishing release JSON schema

All of the release related JSON documents now have JSON schema available[^1], but as far as I can tell they aren't published anywhere. They are available on `raw.githubusercontent.com`. For example: https://raw.githubusercontent.com/dotnet/core/refs/heads/main/release-notes/schemas/dotnet-releases-index.json. But `raw.githubusercontent.com` shouldn't be used as a CDN.

Additionally, if they were published the `$schema` property could be added to each JSON document. And the existing `$schema` property in `releases-index.json`[^2], pointing to a community-supported JSON schema[^3], could be replaced with the officially-supported one.

[^1]: https://github.com/dotnet/core/tree/main/release-notes/schemas
[^2]: https://github.com/dotnet/core/blob/main/release-notes/releases-index.json
[^3]: https://github.com/SchemaStore/schemastore/blob/master/src/schemas/json/dotnet-releases-index.json