Add script to fetch OpenJDK 21 prebuilts am: f849b278a3 am: 6132427422 am: 4eb84dd809

Original change: https://android-review.googlesource.com/c/platform/prebuilts/jdk/jdk21/+/2850965

Change-Id: I7ffc87a977a6391c122c87ac40f08254aeb03fd2
Signed-off-by: Automerger Merge Worker <[email protected]>