6-days Structured Data's DAGs timeout & DagProperties

As DAGs have a weekly schedule and the image suggestions one computes a diff between the current and the previous runs, we set a 6-days timeout to avoid concurrent execution, typically due to upstream data generation failures. This should mitigate the risk of broken diffs that would impact target search indices.

This commit also replaces deprecated VariableProperties with DagProperties, thus enabling more flexixble DAG and operators changes, plus making the DAG code more readable.

Bug: T339351