Update the Events/Agenda shortcode to allow for multiple agenda for an event

In updating the SAM IoT event using the template, we hit a new use-case where there are multiple days or multiple agendas to display. We should create a visual styling or plan to handle this case as it is a common use-case for events. Below is the current workaround which isn't ideal but works for the moment:

This can be fixed in 1 of two ways:

1. Add an src parameter to allow for multiple defined agendas in a given event, and create a visual styling for how to display multiple agenda's on the page.
2. Update the structure of the agenda data to allow for multiple sets of sessions. This should be done in a way that does not break current agendas, and instead adds a new possible feature.