migrations: add package_symbols.id_bigint

The rate of growth for the package_symbols table suggests that the id
column might hit the INTEGER limit as the size of our database grows. We
change this to a BIGINT column now, since its easier to make this change
before this table is used in prod.

Change-Id: Ia2f31d87b97392d2ff83c8a2e07ebad6076ee9fe
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/302669
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

migrations/000082_add_package_symbols_bigint.down.sql

@@ -0,0 +1,13 @@
+-- Copyright 2021 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 documentation_symbols
+    ADD CONSTRAINT documentation_symbols_package_symbol_id_fkey
+    FOREIGN KEY (package_symbol_id) REFERENCES package_symbols(id);
+
+ALTER TABLE package_symbols DROP COLUMN id_bigint;
+
+END;

migrations/000082_add_package_symbols_bigint.up.sql

@@ -0,0 +1,10 @@
+-- Copyright 2021 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 documentation_symbols DROP CONSTRAINT documentation_symbols_package_symbol_id_fkey;
+ALTER TABLE package_symbols ADD COLUMN id_bigint bigint;
+
+END;