Plugins: Create single point of entry for adding / removing plugins (#55463)

* split out plugin manager

* remove whitespace

* fix tests

* split up tests

* updating naming conventions

* simplify manager

* tidy

* explorations

* fix build

* tidy

* fix tests

* add logger helper

* pass the tests

* tidying

* fix tests

* tidy and re-add test

* store depends on loader

* enrich tests

* fix test

* undo gomod changes

pkg/plugins/config/config.go

@@ -14,6 +14,8 @@ type Cfg struct {
 
 	DevMode bool
 
+	PluginsPath string
+
 	PluginSettings       setting.PluginSettings
 	PluginsAllowUnsigned []string
 
@@ -52,6 +54,7 @@ func NewCfg(settingProvider setting.Provider, grafanaCfg *setting.Cfg) *Cfg {
 
 	return &Cfg{
 		log:                     logger,
+		PluginsPath:             grafanaCfg.PluginsPath,
 		BuildVersion:            grafanaCfg.BuildVersion,
 		DevMode:                 settingProvider.KeyValue("", "app_mode").MustBool(grafanaCfg.Env == setting.Dev),
 		EnterpriseLicensePath:   settingProvider.KeyValue("enterprise", "license_path").MustString(grafanaCfg.EnterpriseLicensePath),