Adding upstream electrons in the tau->mu gamma lines

Adding upstream electrons for the soft gamma reconstruction in the \tau\rightarrow \mu \gamma lines. Given the nature of this decay, upstream 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 [KB/s]	expect. bw [KB/s]
Hlt2RD_TauToMuGamma_EE	5.72	5.73	6.485	6.501
Hlt2RD_TauToMuGamma_EE_MVA	9.62	9.64	6.507	6.524

Also, as can be seen in the next plot, upstream electron tracks give nonnegligible contributions.