Add size to Save function (#15264) (#15271)

Backport #15264

This PR proposes an alternative solution to #15255 - just add the size to the
save function. Yes it is less apparently clean but it may be more correct.

Close #15255
Fix #15253

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

integrations/attachment_test.go

@@ -122,7 +122,7 @@ func TestGetAttachment(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			//Write empty file to be available for response
 			if tc.createFile {
-				_, err := storage.Attachments.Save(models.AttachmentRelativePath(tc.uuid), strings.NewReader("hello world"))
+				_, err := storage.Attachments.Save(models.AttachmentRelativePath(tc.uuid), strings.NewReader("hello world"), -1)
 				assert.NoError(t, err)
 			}
 			//Actual test