```trivy image``` support auth parameterization when use self hosted repo

[afghanistanyn]

1. Using env TRIVY_USERNAME,TRIVY_PASSWORD is too difficult when i hava to scan a lot of image from diffrent repo.
2. i integrate trivy to my app , to set diffrent auth info, i have to rewrite runner.ScanImage()

i hope DockerConfig or DockerOption add to flag.Options