Alerts related to Gatus to know when analysis sites are down

[tiffanychu90]

User story / feature request

Please describe your need, outlining the key users, the feature being requested, and the goal that that the feature will facilitate. As a data analyst, I want to know when the individual sites on the analysis.calitp.org are down. Jarvus set up https://gatus.jarv.us/ to help monitor various sites, but I would like an alert to show up in a Slack channel when something is down.

Acceptance Criteria

Some type of alert is sent to Slack (or other method) when a site becomes broken.