[Feature] support plugin level config

[yeshan333]

1. Your usage scenarios?

• let plugin developer can load config in one-place.
  • some plugin would load option from PATH environment. This mechanism causes these configurations to be scattered in various places, and it is difficult to troubleshoot problems when they occur.

2. What is your expected outcome?

the plugin can load configs from vfox global config (relate issue: https://github.com/version-fox/vfox/issues/301).