This is a Tekton EventListener interceptor that can turnaround Slack "slash command" requests into JSON for further processing.
See this https://bigkevmcd.github.io/tekton/triggers/slack/commands/2020/03/02/slack-slash-tekton.html for detailed instructions.
See this example EventListener for how to use this, it shows an EventListener that uses the interceptor to drive a TaskRun that outputs the command and details.