* tsdb: Expose total number of label pairs in head Signed-off-by: Nguyen Le Vu Long <vulongvn98@gmail.com> * fix: add comment for NumLabelPairs Signed-off-by: Nguyen Le Vu Long <vulongvn98@gmail.com> * fix: remove comment Signed-off-by: Nguyen Le Vu Long <vulongvn98@gmail.com>