Update API endpoint to account for 90-day rolling points

[j4rodm]

Currently there is only one endpoint, which only looks at the grand total, not the 90-day rolling total.

https://devprogramresources.service-now.com/api/x_snc_slack_points/handle_slack_events/leaderboard?top=5

Also, recommend changing the API name to be shorter, maybe remove 'handle_slack_events'?