Fix runtime crate versions (#3260)

## Motivation and Context
When the stable/unstable crate versions were split, this caused a
regression in determining the crate version during codegen. This
enhances our crate-version forwarding code to publish all the crate
versions. For impact, see codegen-client-test.

## Description
- Change the build artifact to be a JSON blob will all required
versions.

## Testing
- [ ] Audit diff

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [ ] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates
- [ ] I have updated `CHANGELOG.next.toml` if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._