Update maintainers
Fabian and Alex are not part of the team any more.
Firecracker is maintained by a dedicated team within Amazon:
- Alexandra Iordache <aghecen@amazon.com>
-- Alexandru-Cezar Sardan <alsardan@amazon.com>
- Andrei-Cristian Traistaru <atc@amazon.com>
-- Anton Fabian Patras <patrsap@amazon.com>
- Babis Chalios <bchalios@amazon.com>
- Diana Popa <dpopa@amazon.com>
- Jonathan Woollett-Light <jcawl@amazon.com>
