Add interface to get version of item

Pass version as UID in OwnerInfo to kopia to allow more control of what
kopia thinks is a cached file.

src/internal/data/data_collection.go

@@ -87,6 +87,10 @@ type StreamModTime interface {
 	ModTime() time.Time
 }
 
+type Versioner interface {
+	Version() uint32
+}
+
 // ------------------------------------------------------------------------------------------------
 // functionality
 // ------------------------------------------------------------------------------------------------

src/internal/kopia/upload.go

@@ -339,9 +339,15 @@ func collectionEntries(
 				modTime = smt.ModTime()
 			}
 
+			o := fs.OwnerInfo{}
+			if sv, ok := e.(data.Versioner); ok {
+				o.UserID = sv.Version()
+			}
+
 			entry := virtualfs.StreamingFileWithModTimeFromReader(
 				encodedName,
 				modTime,
+				o,
 				newBackupStreamReader(serializationVersion, e.ToReader()),
 			)
 			if err := cb(ctx, entry); err != nil {