Starboard Vulnerability scan fails to process scan job when auth is missing in registry secret

[Devendra Turkar]

If user creates a registry secret without auth mentioned in it, then starboard fails with error
error: reading .dockerconfigjson field of "xx/xx-registry" secret: expected username and password concatenated with a colon (:)
even though registry secret has username and password specified in dockerconfigjson, auth part is missing in the detail.
eg:

"harbor.domain": {
Username: "admin",
Password: "Harbor12345",
}

We can add additional logic to consider username and password if auth is empty.