Add multiple Dockerfiles for various Gitea runner profiles and update host vars

ansible/files/dockerfiles/linux-runners/Dockerfile.image-build

@@ -0,0 +1,32 @@
+FROM local/gitea-runner-base:latest
+
+# image-build runner profile: dedicated environment for container image builds.
+USER root
+RUN apk add --no-cache \
+	bash \
+	buildah \
+	ca-certificates \
+	curl \
+	fuse-overlayfs \
+	git \
+	iptables \
+	jq \
+	make \
+	openssh-client \
+	podman \
+	python3 \
+	py3-pip \
+	rsync \
+	shadow-uidmap \
+	skopeo \
+	slirp4netns \
+	unzip \
+	yq \
+	zip
+
+RUN mkdir -p /etc/containers /var/lib/containers /run/containers && \
+	printf '%s\n' '[storage]' 'driver = "vfs"' > /etc/containers/storage.conf && \
+	printf '%s\n' '[engine]' > /etc/containers/containers.conf
+
+ENV BUILDAH_ISOLATION=chroot
+ENV STORAGE_DRIVER=vfs