Unified Storage Indexer: Build tenant indexes concurrently (#95795)

* WIP - build tenant indexes concurrently

* adds local dev seeders and readme for indexer

* update logging and adds locking in getShard()

* update logs

* Adds Namespaces func. Initializes index after ResourceServer is created.

* fixes Count() and updates test lint issues

* Initialize index separately. Don't do it when creating the resource server. Makes testing really awkward.

* fix lint error

* handles error when getting namespaces

* updates test and index helper funcs

pkg/storage/unified/resource/server.go

@@ -75,6 +75,8 @@ type StorageBackend interface {
 	// Get all events from the store
 	// For HA setups, this will be more events than the local WriteEvent above!
 	WatchWriteEvents(ctx context.Context) (<-chan *WrittenEvent, error)
+
+	Namespaces(ctx context.Context) ([]string, error)
 }
 
 // This interface is not exposed to end users directly
@@ -182,7 +184,7 @@ func NewResourceServer(opts ResourceServerOptions) (ResourceServer, error) {
 			UserID:         1,
 			IsGrafanaAdmin: true,
 		}))
-	return &server{
+	s := &server{
 		tracer:      opts.Tracer,
 		log:         logger,
 		backend:     opts.Backend,
@@ -194,7 +196,9 @@ func NewResourceServer(opts ResourceServerOptions) (ResourceServer, error) {
 		now:         opts.Now,
 		ctx:         ctx,
 		cancel:      cancel,
-	}, nil
+	}
+
+	return s, nil
 }
 
 var _ ResourceServer = &server{}
@@ -765,6 +769,10 @@ func (s *server) Origin(ctx context.Context, req *OriginRequest) (*OriginRespons
 
 // Index returns the search index. If the index is not initialized, it will be initialized.
 func (s *server) Index(ctx context.Context) (*Index, error) {
+	if err := s.Init(ctx); err != nil {
+		return nil, err
+	}
+
 	index := s.index.(*IndexServer)
 	if index.index == nil {
 		err := index.Init(ctx, s)