add phabricator genAI funnel logging

Summary:
Log the SHOWN event for the metamate generated suggestion to the phab genAI funnel. Note that this diff along won't send the data to our funnel event table. I still need to land a change to the XStream pipeline https://fburl.com/code/q4r3mtrv to get it fully functioning.

Instead of creating seperate ISL events for the funnel logging I think it'd be easier to just have one event for it. One I got everything working e2e I can migrate the summary testplan genAI logging to this as well.

Reviewed By: evangrayk

Differential Revision: D66797058

fbshipit-source-id: bf41d644919e9a0f0bfa557fbaf5e89a79b90251

addons/isl-server/src/analytics/eventNames.ts

@@ -86,6 +86,7 @@ export type TrackEventName =
   | 'PartialCommitOperation'
   | 'PartialAmendOperation'
   | 'PartialDiscardOperation'
+  | 'PhabricatorGenAIFunnelEvent'
   | 'PrSubmitOperation'
   | 'PullOperation'
   | 'PullRevOperation'