missing imagePullSecrets when using custom private image registry

[bingwei-hong-partior]

After chaosCenter is configured to use private image registry, when use litmusctl to connect new delegate, it will get the images from the new private registry, however imagePullSecrets tag is missing from the generated deployment, result in all imagepull failure.

This issue can be easily replicated by change the image registry to a private registry in chaosCenter, then try with a litmusctl connect.