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/test/indexer_integration_test.go

@@ -77,7 +77,7 @@ func TestIntegrationIndexerSearch(t *testing.T) {
 	addResource(t, ctx, backend, "playlists", playlist1)
 	addResource(t, ctx, backend, "playlists", playlist2)
 
-	// initialze and build the search index
+	// initialize and build the search index
 	indexer, ok := server.(resource.ResourceIndexer)
 	if !ok {
 		t.Fatal("server does not implement ResourceIndexer")