SCB-2176 Decompose the plugin and server pkg

[little-cui]

重构背景

1. server/plugin/plugin.go本身的设计初衷是作为公共的插件管理器，但由于实现中依赖了server/config包，形成了公共库反向依赖组件server的问题。

2. 分析了依赖config的原因，在插件实例化过程中，需要提供一个插件实现名字来定义管理器生成的插件实例，当前实现是通过server的配置读取的。

// server/plugin/plugin.go
name := config.GetString(pn.String()+".kind", Buildin, config.WithStandby(pn.String()+"_plugin"))
p, ok = m[ImplName(name)]

解决方案

1. 依赖反转，plugin提供新的接口，负责插件的业务自定义配置pkg/plugin/types.go 的Configurator，自身也提供默认实现 pkg/plugin/config.go 的DefaultConfigurator

// Configurator provides the interfaces for obtaining configs in
// plugin mgr's operations, user can customize the impl
type Configurator interface {
	GetImplName(kind Kind) string
	GetPluginDir() string
}

2. server侧实现Configurator接口，server/config/types.go 的 Config。在Init阶段注册到插件管理器

plugin.RegisterConfigurator(Configurations)

3. 完成1-2后，plugin可以从server中解耦出来。

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[tianxiaoliang]

please claim your motivation and solution