Registry flag should accept protocol

[Jonathan Juares Beber]

The push image-bundle command's flag --to-registry should accept http or https as a prefix.

Currently the command just fails with an unclear message:

mindthegap push image-bundle --image-bundle ./bundle.tar --to-registry https://myregistry.jbeber.com:5000 --to-registry-ca-cert-file=registry/ca.crt
 ✓ Creating temporary directory
 ✓ Unarchiving image bundle "./bundle.tar" 
 ✓ Parsing image bundle config
 ✓ Starting temporary Docker registry
---skopeo stdout---:

---skopeo stderr---:
time="2022-11-01T21:09:20Z" level=fatal msg="not logged into myregistry.jbeber.com:5000"

error logging in to target registry: failed to check if already logged in to https://myregistry.jbeber.com:5000: exit status 1

with --to-registry myregistry.jbeber.com:5000 it works.