onboarding improvements

[DennisDenuto]

Worked with @seemiller

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

• ui vs logger -> hard to make changes since there are 2 different logging mechanisms. Standardize the logging mechanism in imgpkg #259
• 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