SLB: Adding upstream and downstream tracks to the Bs -> Ds* l nu line

Adding upstream and downstream electrons for the soft gamma reconstruction in the B_s0 -> D*s(-> Ds(-> K K pi) gamma (-> ee) ) mu nu line. Given the nature of this decay, upstream and downstream electrons are also suitable for reconstructing the soft gamma.

The expected changes were calculated running over 100K expected_2024_min_bias_hlt1_filtered_v2 events and are summarized in the following table:

line	rate reference [Hz]	expect. rate [Hz]	bw reference [MB/s]	expect. bw [MB/s]
Hlt2SLB_Dst2DsGamma_Ds2KKPi_Gamma2EE	16	18	1.7	2.5