[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/backendplugin/provider/provider.go

@@ -0,0 +1,48 @@
+package provider
+
+import (
+	"context"
+	"path/filepath"
+
+	"github.com/grafana/grafana/pkg/infra/log"
+	"github.com/grafana/grafana/pkg/plugins"
+	"github.com/grafana/grafana/pkg/plugins/backendplugin"
+	"github.com/grafana/grafana/pkg/plugins/backendplugin/grpcplugin"
+	"github.com/grafana/grafana/pkg/plugins/backendplugin/pluginextensionv2"
+)
+
+type Service struct{}
+
+func ProvideService() *Service {
+	return &Service{}
+}
+
+func (*Service) BackendFactory(ctx context.Context, p *plugins.Plugin) backendplugin.PluginFactoryFunc {
+	for _, provider := range []PluginBackendProvider{RendererProvider, DefaultProvider} {
+		if factory := provider(ctx, p); factory != nil {
+			return factory
+		}
+	}
+	return nil
+}
+
+// PluginBackendProvider is a function type for initializing a Plugin backend.
+type PluginBackendProvider func(_ context.Context, _ *plugins.Plugin) backendplugin.PluginFactoryFunc
+
+var RendererProvider PluginBackendProvider = func(_ context.Context, p *plugins.Plugin) backendplugin.PluginFactoryFunc {
+	if !p.IsRenderer() {
+		return nil
+	}
+	cmd := plugins.ComposeRendererStartCommand()
+	return grpcplugin.NewRendererPlugin(p.ID, filepath.Join(p.PluginDir, cmd),
+		func(pluginID string, renderer pluginextensionv2.RendererPlugin, logger log.Logger) error {
+			p.Renderer = renderer
+			return nil
+		},
+	)
+}
+
+var DefaultProvider PluginBackendProvider = func(_ context.Context, p *plugins.Plugin) backendplugin.PluginFactoryFunc {
+	cmd := plugins.ComposePluginStartCommand(p.Executable)
+	return grpcplugin.NewBackendPlugin(p.ID, filepath.Join(p.PluginDir, cmd))
+}