Flatpak delta manifests support

[MichalPysik]

Added Flatpak deltas to the defaultly supported OCI media types.

closes #1495

[ipanova]

Specs say that manifest should be of special delta type as well, this would be great to clarify with the authors, and if confirmed then this would require us to add it to the DB manifests media type choices, and update the json schema validator

[lubosmj]

This might collide with #1533. We are leaving this in draft for now until the referenced PR gets merged.

[lubosmj]

After merging 7ace741 and d6201aa, we no longer need to deal with ADDITIONAL_OCI_ARTIFACT_TYPES.

Please, rebase your PR and make sure that
vnd.redhat.delta.manifest.v1+json (https://github.com/flatpak/flatpak-oci-specs/blob/main/image-deltas.md#locating-the-delta-manifest) is included in

pulp_container/pulp_container/app/models.py

Line 86 in d6201aa

MANIFEST_CHOICES = (

.

I wonder if we should add the media type to

pulp_container/pulp_container/app/json_schemas.py

Line 89 in d6201aa

"enum": [MEDIA_TYPE.MANIFEST_OCI],

and

pulp_container/pulp_container/app/json_schemas.py

Line 53 in d6201aa

allowed_media_types=[

. It is worth to investigate this.

[ipanova]

I doubt that vnd.redhat.delta.manifest.v1+json is being used despite what's written in docs. The documentation still references that this delta manifest is an OCI manifest(and it has predefined mediatypes).

[lubosmj]

https://github.com/flatpak/flatpak-oci-specs/pull/5/files being merged, I think we can safely close this PR and the corresponding issue because everything should work out of the box.

@MichalPysik, thanks for dedicating your efforts into this work. We appreciate your endeavor.