[WIP] Plugins: Refactoring backend initialization flow (#42247)

* refactoring store interface and init flow

* fix import

* fix linter

* refactor resource calling

* load with class

* re-order args

* fix tests

* fix linter

* remove old creator

* add custom config struct

* fix some tests

* cleanup

* fix linter

* add connect failure error

* remove unused err

* convert test over

pkg/plugins/ifaces.go

@@ -34,10 +34,10 @@ type AddOpts struct {
 // Loader is responsible for loading plugins from the file system.
 type Loader interface {
 	// Load will return a list of plugins found in the provided file system paths.
-	Load(paths []string, ignore map[string]struct{}) ([]*Plugin, error)
+	Load(ctx context.Context, class Class, paths []string, ignore map[string]struct{}) ([]*Plugin, error)
 	// LoadWithFactory will return a plugin found in the provided file system path and use the provided factory to
 	// construct the plugin backend client.
-	LoadWithFactory(path string, factory backendplugin.PluginFactoryFunc) (*Plugin, error)
+	LoadWithFactory(ctx context.Context, class Class, path string, factory backendplugin.PluginFactoryFunc) (*Plugin, error)
 }
 
 // Installer is responsible for managing plugins (add / remove) on the file system.
@@ -65,6 +65,11 @@ type Client interface {
 	CollectMetrics(ctx context.Context, pluginID string) (*backend.CollectMetricsResult, error)
 }
 
+// BackendFactoryProvider provides a backend factory for a provided plugin.
+type BackendFactoryProvider interface {
+	BackendFactory(ctx context.Context, p *Plugin) backendplugin.PluginFactoryFunc
+}
+
 type RendererManager interface {
 	// Renderer returns a renderer plugin.
 	Renderer() *Plugin