Generate message about core and contrib changelogs based on builder manifest

[mx-psi]

On #529 we added an automatic link to core and contrib changelogs on the release, see e.g. https://github.com/open-telemetry/opentelemetry-collector-releases/releases/tag/v0.102.0

On the v0.103.x release cycle, we had to do a bugfix release on this repository, since the manifest for the k8s distribution was incorrect. On the v0.103.1 release, we released artifacts that had v0.103.0 core and contrib components, but the release text linked to the (nonexisting) v0.103.1 tag on core and contrib. This was reported by @arminru and was fixed quickly, but we can automate this edge case.

A way to fix this would be to check the versions of components in the manifests instead of the tag value. We would likely need to add a previous check to ensure consistency across versions in the manifests