Akihiro Suda e1967bb9da dockerfile2llb: emit base image config ...

The base image config will be used later for avoiding applying
`SOURCE_DATE_EPOCH` to the base image layers (issue 4614).

The exporter stores this as the `ExporterImageBaseConfigKey` metadata.

NOTE: For a multi-stage Dockerfile like below, the base image refers to
`busybox`, not to `foo`:
```dockerfile
FROM busybox AS foo
FROM foo AS bar
```

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

2024-02-24 05:43:00 +09:00

..

main.go

dockerfile2llb: emit base image config

2024-02-24 05:43:00 +09:00