Use summarize or a new Pipeline object to generate graphs and auto image export

It would be great to create a function or an abstraction of the pipeline object, using apps as node to create a graph, allowing to automatically create png or mermaid or graphviz export.
We could accomplish this using external lib / optional dependency pydot.

We could add a OTBObject.pipeline attr to manage chain of apps and keep link with parents. Not sure this is necessary since we have summarize, but it could be enhanced.