Use DAG serializer for pipelines controller

What does this MR do?

Related to #215524 (closed)

Closes #217813 (closed)

In !31324 (merged) we have introduced a new serializer for DAG pipeline visualization.

In this MR we are wiring it to the PipelinesController#dag.json endpoint.

This MR is bases on top of !31324 (merged)

Does this MR meet the acceptance criteria?

Conformity

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