Add Podman as a Docker replacement.

Add Podman, Buildah and Skopeo as replacements for Docker (not removing
Docker yet). Also, update the Bats image to the latest Alpine release.

images/bats/Dockerfile

-FROM registry.hub.docker.com/library/alpine:3.14
+FROM registry.hub.docker.com/library/alpine:3.17
 # hadolint ignore=DL3018
 RUN apk add --update --no-cache \
         bats \
@@ -7,5 +7,6 @@ RUN apk add --update --no-cache \
         git \
         openssh-client-default \
         openssl \
+        podman \
     && \
     rm -rf /var/cache/apk/* /tmp/* /var/tmp/*

images/docker/Dockerfile

 FROM docker:20.10
 # hadolint ignore=DL3018
 RUN apk add --update-cache --no-cache \
+        buildah \
         docker-compose \
         docker-py \
+        podman \
         py3-dotenv \
         py3-pip \
+        skopeo \
     && \
     python3 -m pip install --no-cache-dir --progress-bar=off deepclean && \
     rm -rf /root/.cache /tmp/* /var/tmp/*