✨ Add support for `lifespan` async context managers (superseding `startup` and `shutdown` events) (#2944)
Co-authored-by: Mike Shantz <mshantz@coldstorage.com>
Co-authored-by: Jonathan Plasse <13716151+JonathanPlasse@users.noreply.github.com>
Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>