[performance] convert enum strings to ints (#3558)

* convert statuses.visibility and notifications.notification_type columns from type string -> int for performance / space savings

* fix test trying to compare string to int

* fix instance count query using string literal instead of gtsmodel const type

* ensure a default value is always set

* also migrate the account settings and sin bin status tables

* initialize maps outside loops and place into singular enum mapping creation func

* use int16 for enum types

* update sinbinstatus creation to be from a snapshot at initial creation

* add snapshot of poll type at creation time

internal/gtsmodel/common.go

@@ -0,0 +1,24 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package gtsmodel
+
+// enumType is the type we (at least, should) use
+// for database enum types. it is the largest size
+// supported by a PostgreSQL SMALLINT, since an
+// SQLite SMALLINT is actually variable in size.
+type enumType int16