CI: add multiarch build / tagging

Adds initial draft of multiarch capability.

For finishing this up we have to:

• add a build runner with following specs to the container-library group (send me the token via Matrix or Signal or whatever :)
• add multiarch features to si shell tooling (interface proposal within draft)

A first successful multiarch on SI-Infrastructure, AWS and Quay.io can be found here https://git.shivering-isles.com/w4tsn/python-mqtt-gpio-container/-/jobs/8563

Runner Specs:

Description: containers-aarch64-autoscale
Tags: aarch64, arm64, armv8, autoscale, aws, ec2, fedora, podman, s3, selinux
Type: docker+machine

resources/shell-tools/bin/manifest-push.sh

+#!/bin/bash
+
+set -o pipefail
+set -u
+set -e
+
+printUsage() {
+    echo "
+    Shivering-Isles push tool
+
+    This tool will push all tagged versions of a container image upstream
+
+    Usage of $0:
+        $0 <IMAGE REFERENCE>
+
+    Example:
+        $0 registry.example.com/example/app:1 registry.example.com/example/app:1.2
+    "
+    exit 1
+}
+
+if [ "$1" = "--help" ]; then
+    printUsage
+fi
+
+DRY=0
+
+for i in "$@"
+do
+case $i in
+    --dry)
+    DRY=1
+    shift
+    ;;
+    -h|--help)
+    printUsage
+    shift
+    ;;
+    *)
+          # further/unknown options
+    ;;
+esac
+done
+
+TAGS_TO_PUSH=("$@")
+
+if [ "$DRY" = "1" ]; then
+    echo "${TAGS_TO_PUSH[@]}"
+else
+    for IMAGE_REFERENCE in "${TAGS_TO_PUSH[@]}"
+    do
+        podman manifest push --all --format v2s2 "$IMAGE_REFERENCE" "docker://$IMAGE_REFERENCE"
+    done
+fi