[BACKEND] - Get all the events from a group (getEventsFromGroup)

[BenReichwein]

^ Follow how we error handle from here

Task:

• In the /db/events.js file add a function getEventsFromGroup with the parameter groupName
• From the Group model get the ID's from the events array
• From the ID's get all the events models and create an array of all of them to be returned