publish: support user-defined metadata

[maxux]

Latest 0-flist now supports metadata settings. Because GitHub doesn't provide a way to accepts inputs not known in advance, it's difficult to let user-defined metadata to be set.

One workaround is specifying a file which would contains metadata. To make things easy because upload script is in bash, it's using environment variable inside a file which would be sourced:

export METADATA_VERSION="2.3.4"
export METADATA_DESCRIPTION="Testing GitHub Actions with flist metadata setter"
export METADATA_HOMEPAGE="http://www.google.com"
export METADATA_USER=$USER
export METADATA_HOSTNAME=$HOST

Snippet to nicely use them:

for entry in $(env | grep ^METADATA_ | awk -F'=' '{ print $1 }'); do
    single=${entry:9}
    key=${single,,}

    echo "$key => ${!entry}"
done

version => 2.3.4
description => Testing GitHub Actions with flist metadata setter
homepage => http://www.google.com
hostname => laptix
user => maxux

This is related to:

• zflist: support generic metadata 0-flist#36
• flist: support metadata (tags) 0-hub#25

GitHub Actions integration would be required for:

• github deprecates ubuntu 18.04 action runner home#1300
• zpkg: a package manager for zos zos#1789 more specifically