Plugins: Update renderer plugin source (#80643)

* rework renderer plugin source

* add tests

pkg/plugins/manager/sources/sources.go

@@ -2,9 +2,7 @@ package sources
 
 import (
 	"context"
-	"os"
 	"path/filepath"
-	"slices"
 
 	"github.com/grafana/grafana/pkg/plugins"
 	"github.com/grafana/grafana/pkg/plugins/log"
@@ -34,33 +32,17 @@ func (s *Service) List(_ context.Context) []plugins.PluginSource {
 }
 
 func (s *Service) externalPluginSources() []plugins.PluginSource {
-	var sources []plugins.PluginSource
-	if s.cfg.PluginsPath == "" {
-		return sources
-	}
-
-	pluginsPath := s.cfg.PluginsPath
-	// It's safe to ignore gosec warning G304 since the variable part of the file path comes from a configuration
-	// variable.
-	// nolint:gosec
-	d, err := os.ReadDir(pluginsPath)
+	localSrcs, err := DirAsLocalSources(s.cfg.PluginsPath, plugins.ClassExternal)
 	if err != nil {
-		s.log.Error("Failed to open plugins path", "path", pluginsPath, "error", err)
-		return sources
+		s.log.Error("Failed to load external plugins", "error", err)
+		return []plugins.PluginSource{}
 	}
 
-	var pluginDirs []string
-	for _, dir := range d {
-		if dir.IsDir() || dir.Type()&os.ModeSymlink == os.ModeSymlink {
-			pluginDirs = append(pluginDirs, filepath.Join(pluginsPath, dir.Name()))
-		}
+	var srcs []plugins.PluginSource
+	for _, src := range localSrcs {
+		srcs = append(srcs, src)
 	}
-	slices.Sort(pluginDirs)
-
-	for _, dir := range pluginDirs {
-		sources = append(sources, NewLocalSource(plugins.ClassExternal, []string{dir}))
-	}
-	return sources
+	return srcs
 }
 
 func (s *Service) pluginSettingSources() []plugins.PluginSource {