* Addon configuration now takes an optional config file to load from
instead of forcing prompts
Fixes#20124
* Using a rarer value for default instead of changeme so it has less chance to interfere with other possible user defaults
* Fixing expected values of test cases
* making addonConfigFile private
* Keeping registry_creds configs together.
* Starting a typed AddonConfig struct so each addon con loads its
configs in a typed way.
* Started configs for RegistryCreds using this convention and moved
registry_creds config processing to its own file
(configure_registry_creds.go)
* Making registry creds structs private and other PR feedback cleanups
* Changing default value back to 'changeme'
* Simplifying duplicate consts
* Adding missed comma
* lint fixes
* Generating docs
* Copyright for new file
minikube-bot
Medya Ghazizadeh
Sri Panyam
Daniel Pepuho