The automated rebuild failed with 'Missing required configuration:
--base-image-id' because the ALIYUN_ECS_BASE_IMAGE_ID repo variable
does not exist yet (it was flagged as a one-time setup item).
Remove the setup dependency instead: build-ecs-image.py now defaults
--base-image-id to the latest public Ubuntu 24.04 x86_64 system image
in the region (DescribeImages with image_owner_alias=system), so no
manual variable is required. The runner Dockerfile pins every tool
version itself, so base-image drift is low-risk; --base-image-id or
the ALIYUN_ECS_BASE_IMAGE_ID variable still pin a specific base image
deterministically, and the workflow only passes the flag when the
variable is set.
Part of #9289.
Signed-off-by: Ning Sun <sunning@greptime.com>