Add public ECR push for clickhouse-ddl to release workflow

[mheffner]

Summary

• Add a docker-push-clickhouse-ddl-ecr job to the release workflow that pushes the clickhouse-ddl image to public ECR at public.ecr.aws/rotel-dev/clickhouse-ddl
• Mirrors the existing docker-push-rotel-ecr job, using the clickhouse-ddl binary and Dockerfile.clickhouse-ddl

Configuration required

• Create a new repo secret AWS_ECR_PUBLIC_CLICKHOUSE_DDL_ROLE_ARN holding the IAM role ARN with push access to the clickhouse-ddl public ECR repository (alias rotel-dev).