draft init --config should overwrite an existing plugin if the name is the same

[michelleN]

For example, the pack-repo command is a default plugin. If in a toml file passed in via config, a user specifies a plugin to install with the name pack-repo the old pack-repo plugin should be removed and replaced with the new one the user specifies

[michelleN]

identified by @bacongobbler in #787

[michelleN]

This is also is little wonky because we don't really list or use pack-repo names. I can dig into this a little further.