[StepSecurity] Apply security best practices

ci/ovs_test_setup/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:22.04
+FROM ubuntu:22.04@sha256:2b7412e6465c3c7fc5bb21d3e6f1917c167358449fecac8176c6e496e5c1f05f
 RUN apt-get -q update && apt-get install -y openvswitch-switch-dpdk
 RUN update-alternatives --set ovs-vswitchd /usr/lib/openvswitch-switch-dpdk/ovs-vswitchd-dpdk
 ##RUN sed -i "/rmmod bridge/d" /usr/share/openvswitch/scripts/ovs-kmod-ctl

ci/ovs_test_setup/testpmd_image/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:22.04
+FROM ubuntu:22.04@sha256:2b7412e6465c3c7fc5bb21d3e6f1917c167358449fecac8176c6e496e5c1f05f
 RUN apt-get -q update && apt-get install -y git vim meson python3-pyelftools libnuma-dev
 RUN git clone https://github.com/DPDK/dpdk.git
 WORKDIR /dpdk/

docker/testpmd/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:22.04
+FROM ubuntu:22.04@sha256:2b7412e6465c3c7fc5bb21d3e6f1917c167358449fecac8176c6e496e5c1f05f
 RUN apt-get -q update && apt-get install -y git vim meson python3-pyelftools libnuma-dev
 RUN git clone https://github.com/DPDK/dpdk.git
 WORKDIR /dpdk/

docker/userspacecni/Dockerfile

@@ -1,4 +1,4 @@
-FROM ligato/vpp-base:23.02 as builder
+FROM ligato/vpp-base:23.02@sha256:e1d8737eeacd2ca662f2d0349d973b9949fa49e7ff6975bb4548d78f4e373cc0 as builder
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 COPY . /root/userspace-cni-network-plugin
 WORKDIR /root/userspace-cni-network-plugin
@@ -14,7 +14,7 @@ RUN make generate-bin
 #End of builder container
 
 # Copy build userspace cni bin to a small deployer container
-FROM alpine:3.18
+FROM alpine:3.18@sha256:eece025e432126ce23f223450a0326fbebde39cdf496a85d8c016293fc851978
 RUN mkdir -p /root/userspace-cni-network-plugin/userspace
 COPY --from=builder /root/userspace-cni-network-plugin/userspace/userspace /root/userspace-cni-network-plugin/userspace/userspace
 CMD ["cp", "-rf", "/root/userspace-cni-network-plugin/userspace/userspace", "/opt/cni/bin"]