Currently users have to manually open and edit ~/.vuerc and by looking at the help message users don't really realize it's there.

We should have a vue config command that allows users to more easily inspect and modify the config (and potentially makes it easier for external tools to access/modify the config via the CLI).

• vue config: prints the resolved full path and content of ~/.vuerc
• vue config get <path> - e.g. vue config get packageManager
• vue config set <path> <value> - e.g. vue config set useTaobaoRegistry false (should handle special case parsing for boolean and number values)
• vue config delete <path> - e.g. deleting a preset: vue config delete preset.foo
• vue config edit - opens ~/.vuerc with the default editor (via EDITOR env var)