migrations: add indexes to version_map

Change-Id: I8da86a74f529b32f79a439837a7b0a85913939b6
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/720358
CI-Result: Cloud Build <devtools-proctor-result-processor@system.gserviceaccount.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>

migrations/000013_add_version_map_indexes.down.sql

@@ -0,0 +1,10 @@
+-- Copyright 2020 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+DROP INDEX idx_version_map_module_id;
+DROP INDEX idx_version_map_module_path;
+
+END;

migrations/000013_add_version_map_indexes.up.sql

@@ -0,0 +1,10 @@
+-- Copyright 2020 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+CREATE INDEX idx_version_map_module_id ON version_map (module_id);
+CREATE INDEX idx_version_map_module_path ON version_map (module_path, resolved_version);
+
+END;