chore: switch database engine to sqlite (fixes #9954) (#9965)

Switch the database from LevelDB to SQLite, for greater stability and
simpler code.

Co-authored-by: Tommy van der Vorst <tommy@pixelspark.nl>
Co-authored-by: bt90 <btom1990@googlemail.com>

lib/config/migrations.go

@@ -208,7 +208,7 @@ func migrateToConfigV23(cfg *Configuration) {
 	// marker name in later versions.
 
 	for i := range cfg.Folders {
-		fs := cfg.Folders[i].Filesystem(nil)
+		fs := cfg.Folders[i].Filesystem()
 		// Invalid config posted, or tests.
 		if fs == nil {
 			continue
@@ -244,18 +244,18 @@ func migrateToConfigV21(cfg *Configuration) {
 		switch folder.Versioning.Type {
 		case "simple", "trashcan":
 			// Clean out symlinks in the known place
-			cleanSymlinks(folder.Filesystem(nil), ".stversions")
+			cleanSymlinks(folder.Filesystem(), ".stversions")
 		case "staggered":
 			versionDir := folder.Versioning.Params["versionsPath"]
 			if versionDir == "" {
 				// default place
-				cleanSymlinks(folder.Filesystem(nil), ".stversions")
+				cleanSymlinks(folder.Filesystem(), ".stversions")
 			} else if filepath.IsAbs(versionDir) {
 				// absolute
 				cleanSymlinks(fs.NewFilesystem(fs.FilesystemTypeBasic, versionDir), ".")
 			} else {
 				// relative to folder
-				cleanSymlinks(folder.Filesystem(nil), versionDir)
+				cleanSymlinks(folder.Filesystem(), versionDir)
 			}
 		}
 	}