Validate json builder schemas for different repo builders

This CL add builder schemas validation, in addition to existing general
json format validation.
Test run: (#6) https://luci-milo.appspot.com/raw/build/logs.chromium.org/flutter/led/keyonghan_google.com/eba590386316264dbcab9fc015bff2eb33445f6d752a8fd9f99dfcffcd546ae3/+/annotations

Bug: https://github.com/flutter/flutter/issues/64366
Change-Id: I592d123e548eba68374bd7e2939ee61d0c9c245d
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/6340
Commit-Queue: Keyong Han <keyonghan@google.com>
Reviewed-by: Tong Wu <wutong@google.com>