kctrl: Accept username and password for the registry from the user interaction and use it to authenticate.

**Describe the problem/challenge you have**

Accept username and password for the registry from the user interaction and use it to authenticate(for imgpkg commands) in `pkg release` and `pkg repo release`.

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Start by locating the kctrl interaction flows for `pkg release` and `pkg repo release`, then trace how they invoke imgpkg commands. Add user-provided registry credentials to those flows and verify that both commands authenticate successfully when publishing to a protected registry.

Written by the indexing model from the issue text.