feat: add cosign to rootfs (#181)

Issue #, if available:

*Description of changes:*
Add cosign binary to rootfs

*Testing done:*


- [X] I've reviewed the guidance in CONTRIBUTING.md


#### License Acceptance

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

---------

Signed-off-by: Vishwas Siravara <[email protected]>

Dockerfile

@@ -18,6 +18,11 @@ RUN dnf install -y \
   iptables \
   fuse-sshfs
 
+# install cosign
+RUN curl -L -O https://github.com/sigstore/cosign/releases/download/v2.0.1/cosign-2.0.1.x86_64.rpm && \
+    sudo rpm -ivh cosign-2.0.1.x86_64.rpm && \
+    rm -rf cosign-2.0.1.x86_64.rpm
+
 RUN systemctl enable cloud-init cloud-init-local cloud-config cloud-final
 
 # enable systemd