Tweak Dockerfile to use dnf4/5 builders

Dockerfile

@@ -1,12 +1,19 @@
 # Example Usage:
 # $ podman build --build-arg TYPE=distro -t ci-dnf-stack -f Dockerfile
 # $ podman run --net none -it ci-dnf-stack behave dnf
+#
+# Build for DNF4
+# $ podman build --build-arg DNF=dnf -t ci-dnf-stack -f Dockerfile
+#
+# Build for a specific Fedora version
+# $ podman build --build-arg BASE=fedora:38 -t ci-dnf-stack -f Dockerfile
 
 ARG BASE=fedora:39
 FROM $BASE
 
 ENV LANG C.UTF-8
 ARG TYPE=nightly
+ARG DNF
 
 # disable deltas and weak deps
 RUN set -x && \
@@ -24,31 +31,33 @@ RUN set -x && \
 
 # enable dnf5
 RUN set -x && \
-    dnf -y copr enable rpmsoftwaremanagement/dnf-nightly; \
-    dnf -y install dnf5-plugins; \
-    # run upgrade before distro-sync in case there is a new version in dnf-nightly that has a new dependency
-    dnf5 -y upgrade; \
-    dnf5 -y distro-sync --repo copr:copr.fedorainfracloud.org:rpmsoftwaremanagement:dnf-nightly;
+    if [ $DNF == "dnf5" ]; then \
+        dnf -y copr enable rpmsoftwaremanagement/dnf-nightly; \
+        dnf -y install dnf5-plugins; \
+        # run upgrade before distro-sync in case there is a new version in dnf-nightly that has a new dependency
+        dnf5 -y upgrade; \
+        dnf5 -y distro-sync --repo copr:copr.fedorainfracloud.org:rpmsoftwaremanagement:dnf-nightly; \
+    fi
 
 RUN set -x && \
     if [ -n "$COPR" ] && [ -n "$COPR_RPMS" ]; then \
-       dnf5 -y copr enable $COPR; \
-       dnf5 -y install $COPR_RPMS; \
+       $DNF -y copr enable $COPR; \
+       $DNF -y install $COPR_RPMS; \
     fi
 
 # copy test suite
 COPY ./dnf-behave-tests/ /opt/ci/dnf-behave-tests
 
 # install test suite dependencies
 RUN set -x && \
-    dnf5 -y builddep /opt/ci/dnf-behave-tests/requirements.spec && \
+    $DNF -y builddep /opt/ci/dnf-behave-tests/requirements.spec && \
     pip3 install -r /opt/ci/dnf-behave-tests/requirements.txt
 
 # install local RPMs if available
 COPY ./rpms/ /opt/ci/rpms/
 RUN rm /opt/ci/rpms/*-{devel,debuginfo,debugsource}*.rpm; \
     if [ -n "$(find /opt/ci/rpms/ -maxdepth 1 -name '*.rpm' -print -quit)" ]; then \
-        dnf5 -y install /opt/ci/rpms/*.rpm --disableplugin=local; \
+        $DNF -y install /opt/ci/rpms/*.rpm --disableplugin=local; \
     fi
 
 # create directory for dbus daemon socket