In the events details view use a dropdown instead of normal input

[tommygonzaleza]

• Change the input of the host value in the event details view (For creating or editing) to a dropdown like the one used in the add a new staff member
• Modify the Event model to add the host_user which value is a user. This property can be null and by default it should be null
• Modify the serializers where the host is returned to include as well the host_user around here. You have to use the serializer for the user, you can check how it was used here
• Change the view as well to validate that the user exists.

Expected time: 6 - 8 hours

[etolopez]

Pr: breatheco-de/admin#339

h: 1.5

[tommygonzaleza]

The dropdown should allow selecting multiple users, modify both backend and frontend