Pendingevent fire action

When a user comes from a campaign builder email campaign where they receive a discount, they'll have a pe_id in their params. This id ties back to a specific record in the PendingEvent model and will call the "fire" method in the PendingEvent model.

Fire evaluates the action on the model, which applies a discount

Note: params are user_id, subscription_discount_id, and email_campaign_tag

This will give the user a discount as specified from the campaign