gfe-relnote: In QUIC BBR(v1 and v2), do not add QuicBandwidth::Zero() into the max bandwidth filter. Protected by --gfe2_reloadable_flag_quic_bbr_fix_zero_bw_on_loss_only_event. This is an attempt to fix b/151239871. PiperOrigin-RevId: 300605878 Change-Id: I0dc04fe0b6735e88777de510bda072da4c2854c6