notifications-utils: 86.0.0 -> 87.0.0??, use thread-local `ZendeskClient`

[risicle]

On the long road to https://trello.com/c/ORGrd1jn/498-upgrade-docker-images-for-our-ecs-apps-to-debian-bookworm

These are basically the api changes needed to handle the breaking changes in https://github.com/alphagov/notifications-utils/pull/1152. Draft because that isn't merged yet.