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/registry/apis/dashboard/legacy/sql_dashboards.go

@@ -131,6 +131,10 @@ type rowsWrapper struct {
 	err error
 }
 
+func (a *dashboardSqlAccess) Namespaces(ctx context.Context) ([]string, error) {
+	return nil, fmt.Errorf("not implemented")
+}
+
 func (r *rowsWrapper) Close() error {
 	if r.rows == nil {
 		return nil