Expose Build Context Variables(i.e SourceImage, SourceImageDate)

#### Description

I am not sure if this is already available but couldn't seen it in the current docs. Basically as AWS build has a way to expose the Build Variables(SourceAMI) that can be injected into labels.

#### Use Case(s)

In a long chain of images is good to have a trace of the source image id from the label metadata.

#### Potential configuration

```
{{.SourceImageName}}
```

#### Potential References
https://github.com/hashicorp/packer-plugin-amazon