Map XPKG annotations to OCI annotations

### What problem are you facing?

The XPKG spec has the concept of [object annotations](https://github.com/crossplane/crossplane/blob/main/contributing/specifications/xpkg.md#object-annotations), which allow specifying package metadata. The OCI spec similarly has certain [pre-defined annotation keys](https://github.com/opencontainers/image-spec/blob/main/annotations.md#pre-defined-annotation-keys).

Right now there is no way to set OCI annotations on artifacts produced by `crossplane project build`. This is addressed by #11, but it requires that you specify both XPKG annotations and OCI annotations.

### How could Crossplane help solve your problem?

Having to specify the same annotations twice for XPKG and OCI is annoying, especially if it's done in two different ways: one via configuration file (`crossplane-project.yaml`) and the other via CLI flag.

There is quite a big overlap between XPKG and OCI annotations. I think it could make sense to map from the former to the later, possibly as an opt-in (for example, `--map-xpkg-to-oci-annotations`). When this is set, it would automatically propagate `meta.crossplane.io/source` to `org.opencontainers.image.source`, etc. The details of this mapping needs to be figured out.

This could be done in addition to manually specifying OCI annotations (i.e. #11). If both are specified, I would expect them to be merged and for the manually specified OCI annotations to take precedence.

Related issues:
- #11
- crossplane/crossplane#7282

Awesome work on the CLI and DevEx tooling by the way!