Submitting a `WorkGraph` from a `WorkChain`

[edan-bainglass]

The docs suggest the following:

class TestWorkChain(WorkChain):
    @classmethod
    def define(cls, spec):
        super().define(spec)
        spec.input_namespace('workgraph', dynamic=True)
        spec.outline(
            cls.run_workgraph,
            cls.results,
        )
        spec.output('sum')
        spec.output('product')

    def run_workgraph(self):
        from aiida_workgraph.engine.workgraph import WorkGraphEngine

        process = self.submit(WorkGraphEngine, **self.inputs.workgraph)  # possible issue
        self.to_context(workgraph_process=process)

    def results(self):
        self.out('sum', self.ctx.workgraph_process.outputs.sum)
        self.out('product', self.ctx.workgraph_process.outputs.product)

But the possible issue I mark is that self.inputs.workgraph may (or does?) carry a process key, which appears to conflict with the one expected by the submit function, for which the example passes the WorkGraphEngine. We may need to assign directly to the workgraph_data key.

Still investigating. Pinging @superstar54 @GeigerJ2