Multi-environment configuration merge support

[greper]

Describe the solution you'd like First , I know go run app.go-f etc/app.yaml can switch config

But I don't want to copy all the configuration in app-prod.yaml

I want to configure only the parts that must be modified in app-prod.yaml and inherit the rest from app.yaml

configs := []*configFiles
conf.MustLoad(configFiles, &c, conf.UseEnv())

We can use loader to load multiple configuration files as json, and then combine the previous configuration with the later configuration, and finally convert into a config struct

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Additional context Add any other context or screenshots about the feature request here.