Consider adding OCI Image Annotations to .NET images

See the list of pre-defined OCI image annotations here:

https://github.com/opencontainers/image-spec/blob/main/annotations.md#pre-defined-annotation-keys

Several of these annotations overlap with our `image-info.json` spec. Of note are:
- **org.opencontainers.image.created**
- **org.opencontainers.image.source**
- **org.opencontainers.image.base.digest**
- **org.opencontainers.image.base.name**

(The base image annotations were added to the spec in [2021](https://github.com/opencontainers/image-spec/commit/71ccc68078c473544315863eabb2f95140f7e1bf))

We have already computed lots of this information when we build our images. We should consider adding these annotation to image manifests in addition to (or instead of) tracking it ourselves in image-info.json files.