Heredoc notation support for Containerfile

[GrabbenD]

Feature request description

Docker recently introduced Heredoc notation for Dockerfile:
https://www.docker.com/blog/introduction-to-heredocs-in-dockerfiles/

Since dockerfile:1.4 it's possible to use this syntax:

# syntax=docker/dockerfile:1
COPY <<EOF /etc/yum.repos.d/Repo.repoxyz
[repo]
name            = YUM Repository
baseurl         = https://example.com/packages/
enabled         = 1
gpgcheck        = 0
EOF

Meanwhile Podman doesn't seem to understand Heredoc notation in Containerfile:

STEP 38/45: COPY <<EOF /etc/yum.repos.d/Repo.repoxyz
Error: building at STEP "COPY <<EOF /etc/yum.repos.d/Repo.repoxyz": checking on sources under "/home": copier: stat: "/<<EOF": no such file or directory

Have you considered any alternatives?

Buildah is still working on this:
containers/buildah#3474

However, technically it should be possible to use this in Podman by using BuildKit for now as outlined here:
https://pythonspeed.com/articles/podman-buildkit/

[flouthoc]

This is duplicate of containers/buildah#3474, please follow issue containers/buildah#3474 for tracking updates on heredoc feature.