support buildah build --push

[willzhang]

Description

support buildah build --push.

i usually build image and run image for test many times, but i must run buildah push after buildah build.

is it possilbe let buildah directly push to remote registry after building an image, like dokcer build --push

buildah build -t docker.io/myrepo/myimage:v1.0 --push=true

Steps to reproduce the issue:
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Describe the results you received:

Describe the results you expected:

Output of rpm -q buildah or apt list buildah:

(paste your output here)

Output of buildah version:

(paste your output here)

Output of podman version if reporting a podman build issue:

(paste your output here)

Output of cat /etc/*release:

(paste your output here)

Output of uname -a:

(paste your output here)

Output of cat /etc/containers/storage.conf:

(paste your output here)

[flouthoc]

Already being worked here: #4677

[flouthoc]

Duplicate of #4671