Feat: Add ability to diagnose `kongctl` configuration settings

Add support for various kongctl configuration features. Useful items would be:

* Ability to diagnose where configuration is loaded from (print config path)
* Ability to get a configuration value and print it to stdout
* Ability to set a configuration value and write it to config path
* Ability to see if a configuration value is read from config, env var, or flag and indicate which is taking precedence

Start by locating kongctl's configuration loading code and CLI entry points. Determine how configuration paths, values, and precedence are currently represented; done should include commands or options that diagnose the source, read values, write values, and report whether config, environment, or flags take precedence.

Written by the indexing model from the issue text.