option to add event markers when plotting BehavioralEvents data

The BehavioralEvents data interface seems to be used for time series with irregular events (https://nwb-schema.readthedocs.io/en/latest/format.html?highlight=events#behavioralepochs). In the example file below, all the data have the same value but the timestamps are irregularly spaced. Adding the option to plot markers+lines could help with visualization (like shown in the nwbwidgets display in the bottom of the picture below)


The example is from `acquisition.lick_times.time_series.lick_left_times` from [this file](https://dandiarchive.s3.amazonaws.com/blobs/063/b97/063b9771-b0c0-4b84-8b7d-fb52929b3087) from dandiset 00006

Reproduce the case using acquisition.lick_times.time_series.lick_left_times from the linked dandiset file and inspect the BehavioralEvents plotting entry point. Determine how the existing plot handles irregular timestamps, then add an option for markers plus lines and verify that the example renders the event markers as shown.

Written by the indexing model from the issue text.