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/sql/queries.go

@@ -55,6 +55,9 @@ var (
 		Isolation: sql.LevelReadCommitted,
 		ReadOnly:  true,
 	}
+	RepeatableRead = &sql.TxOptions{
+		Isolation: sql.LevelRepeatableRead,
+	}
 )
 
 type sqlResourceRequest struct {