Due to changes in the gerrit API, internal cherry-pick bot logic for listening to events on other changes has broken.

The API changed the root-level `.id` field to use a new format of `repo~change_number`, but the listener setup relies on the format `repo~branch~change_id`. The bot must be updated to use the new `.triplet_id` field from queried changes. The event stream still does not deliver a triplet id, even though the API specification states that a ChangeInfo object is used which should be the same as the REST API, so we must continue to construct the triplet id for incoming events.

Note: while it should be possible to use the new two-part format, it's likely safer in the bot to refactor using the triplet id, as significant logic is based upon parsing the triplet ID for needed information points.