Add cron method to gc LFS MetaObjects (#22385)

This PR adds a task to the cron service to allow garbage collection of
LFS meta objects. As repositories may have a large number of
LFSMetaObjects, an updated column is added to this table and it is used
to perform a generational GC to attempt to reduce the amount of work.
(There may need to be a bit more work here but this is probably enough
for the moment.)

Fix #7045

Signed-off-by: Andrew Thornton <art27@cantab.net>

models/migrations/v1_19/v238.go

@@ -0,0 +1,27 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_19 //nolint
+
+import (
+	"code.gitea.io/gitea/modules/timeutil"
+
+	"xorm.io/xorm"
+)
+
+// AddUpdatedUnixToLFSMetaObject adds an updated column to the LFSMetaObject to allow for garbage collection
+func AddUpdatedUnixToLFSMetaObject(x *xorm.Engine) error {
+	// Drop the table introduced in `v211`, it's considered badly designed and doesn't look like to be used.
+	// See: https://github.com/go-gitea/gitea/issues/21086#issuecomment-1318217453
+	// LFSMetaObject stores metadata for LFS tracked files.
+	type LFSMetaObject struct {
+		ID           int64              `xorm:"pk autoincr"`
+		Oid          string             `json:"oid" xorm:"UNIQUE(s) INDEX NOT NULL"`
+		Size         int64              `json:"size" xorm:"NOT NULL"`
+		RepositoryID int64              `xorm:"UNIQUE(s) INDEX NOT NULL"`
+		CreatedUnix  timeutil.TimeStamp `xorm:"created"`
+		UpdatedUnix  timeutil.TimeStamp `xorm:"INDEX updated"`
+	}
+
+	return x.Sync(new(LFSMetaObject))
+}