migrations: add search_documents.path_id column

A search_documents.path_id column is added, which will become a FK to
the paths table.

For golang/go#39629

Change-Id: I4c24c1f93229afb758d4ca0a451fd3a4f6d01f0b
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/265248
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>

migrations/000042_add_search_documents_path_id.down.sql

@@ -0,0 +1,9 @@
+-- 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;
+
+ALTER table search_documents DROP COLUMN path_id;
+
+END;

migrations/000042_add_search_documents_path_id.up.sql

@@ -0,0 +1,9 @@
+-- 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;
+
+ALTER table search_documents ADD COLUMN path_id integer;
+
+END;