Remove `spec.source.image` fields related to image registry client config

[joelanford]

We plan to have a larger design after v1.0.0 that covers how image registry interactions will work. As such, we should not commit to specific API fields that configure API interactions prior to that design being complete. Therefore, we should remove:

• spec.source.image.insecureSkipTLSVerify
• spec.source.image.pullSecret

Removing these fields is likely to break e2e tests that depend on them, so the scope of this issue include fixing up any e2e tests that fail, which likely entails:

• Somehow provide a custom /etc/containers for our e2e that configures insecureSkipTLSVerify in registries.conf and containers-auth.json for any e2e registries we run

[LalatenduMohanty]

#369 has merged. Hence closing this issue.