###Acceptance Criteria:
- Add event goals as a parameter to EventFactory and implement validation for them
- Given that an organizer does not select one of the goal metrics from the dropdown, but they add a goal number, and then they try to save, they should see the following message at the top:
--- "You must add a goal metric and target number in order to save an event goal."
- Given that an organizer selects a goal types from the dropdown, but they do not add a goal number, and then they try to save, they should see the following message at the top:
--- "You must add a goal metric and target number in order to save an event goal."
- Given API users send an invalid goal metric, Then and error message with the text below will be returned
- "You must choose a valid goal metric."
- Given API users send an invalid goal target (not a positive integer or null), Then and error message with the text below will be returned
- "Goal target number must be a positive number."