add upgrade.log

The upgrade from V9 uses this to avoid an automatic upgrade until 1 year
after the V9 update. It can also be used in future such situations.

Sponsored-by: Dartmouth College's Datalad project

Annex/Locations.hs

@@ -1,6 +1,6 @@
 {- git-annex file locations
  -
- - Copyright 2010-2021 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2022 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -44,6 +44,8 @@ module Annex.Locations (
 	gitAnnexFsckDbDirOld,
 	gitAnnexFsckDbLock,
 	gitAnnexFsckResultsLog,
+	gitAnnexUpgradeLog,
+	gitAnnexUpgradeLock,
 	gitAnnexSmudgeLog,
 	gitAnnexSmudgeLock,
 	gitAnnexMoveLog,
@@ -345,6 +347,13 @@ gitAnnexFsckResultsLog :: UUID -> Git.Repo -> RawFilePath
 gitAnnexFsckResultsLog u r = 
 	gitAnnexDir r P.</> "fsckresults" P.</> fromUUID u
 
+{- .git/annex/upgrade.log is used to record repository version upgrades. -}
+gitAnnexUpgradeLog :: Git.Repo -> RawFilePath
+gitAnnexUpgradeLog r = gitAnnexDir r P.</> "upgrade.log"
+
+gitAnnexUpgradeLock :: Git.Repo -> RawFilePath
+gitAnnexUpgradeLock r = gitAnnexDir r P.</> "upgrade.lck"
+
 {- .git/annex/smudge.log is used to log smudges worktree files that need to
  - be updated. -}
 gitAnnexSmudgeLog :: Git.Repo -> RawFilePath