A oras client of Base jib

**Description of the issue**:

Hi team, i want to write a [oras](https://oras.land/) client of base Jib-core, and i need to this feature for it at least:

- custom `Content-Type` for push request
- pull bolb for custom mediaType

I have check the object of `Jib` `JibContainer` `JibContainerBuilder` and have not some public method for this case, it is possible to this case? Thanks any help and remind me if i missed something. :)

Hope it's clear