Extract search users functions into a service (#39002)

* Extract search users to a new service

* Fix wire provider

* Fix common_test and remove RouteRegister

* Remove old endpoints

* Fix test

* Add indexes to dashboards and orgs tables

* Fix lint

pkg/services/sqlstore/migrations/org_mig.go

@@ -41,6 +41,7 @@ func addOrgMigrations(mg *Migrator) {
 		Indices: []*Index{
 			{Cols: []string{"org_id"}},
 			{Cols: []string{"org_id", "user_id"}, Type: UniqueIndex},
+			{Cols: []string{"user_id"}},
 		},
 	}