onboarding improvements

Worked with @seemiller

we have identified the following areas of improvement to help folk onboard and make contributions to imgpkg:

- [x] ui vs logger -> hard to make changes since there are 2 different logging mechanisms. https://github.com/vmware-tanzu/carvel-imgpkg/pull/259
- [x] prefixlogger vs levellogger in copy.go (2 different loggers used)
- [ ] Document the different hack/test scripts
- [ ] Have a friendly way to choose which test suites to run
- [ ] Add documentation around when to use a fake registry vs a real registry within a test
- [ ] Add documentation for folk using intellij / goland on how to run E2E tests to run locally (Setting env variables such as the location of the binary and the other E2E envs
- [ ] use docker golang image to build and run tests locally