Add goCue_time or choice_time line to the plot

**Is your feature request related to a problem? Please describe.**
This is not a problem but rather a feature request on existing function pf.plot_fip_psth_compare_alignments() which has options to align fip signals to either the go cue or the choice timepoints. Both of which are set to time 0. However, in either case there isn't an option to plot the averaged choice or go cue timepoints in the same plot.

**Describe the solution you'd like**
Please add an option to plot the averaged choice or go cue timepoints as a vertical dashed line in the same plot. The dashed line color needs to be tunable, but can be set to grey (alpha=0.3) by default.

**Describe alternatives you've considered**
NA.

**Additional context**
NA.