annex.autocommit can be configured via git-annex config

... to control the default behavior in all clones of a repository.

This includes a new Configurable data type, so the GitConfig type indicates
which values can be configured this way.

The implementation should be quite efficient; the config log is only read
once, and only when a Configurable value has not already been set by
git-config.

Indeed, it would be nice in the future to extend this, so that git-config
is itself only read on demand. Some commands may not need to look at the
git configuration at all.

This commit was sponsored by Trenton Cronholm on Patreon.

Assistant/Threads/Watcher.hs

@@ -42,6 +42,7 @@ import Annex.InodeSentinal
 import Git.Types
 import Git.FilePath
 import Config
+import Config.GitConfig
 import Utility.ThreadScheduler
 import Logs.Location
 import qualified Database.Keys
@@ -83,7 +84,7 @@ instance E.Exception WatcherControl
 
 watchThread :: NamedThread
 watchThread = namedThread "Watcher" $
-	ifM (liftAnnex $ annexAutoCommit <$> Annex.getGitConfig)
+	ifM (liftAnnex $ getGitConfigVal annexAutoCommit)
 		( runWatcher
 		, waitFor ResumeWatcher runWatcher
 		)