Add a way to view `parallel(parallel())` pipeline graph (nested)

[araffin]

What feature do you want to see added?

See #793 (comment)

To reproduce:

node('default') {
    stage('Top level') {
        // outer parallel: two branches
        parallel(
            // First top-level branch
            BranchA: {
                stage('Branch A') {
                    echo "Starting Branch A"

                    // inner parallel inside Branch A
                    parallel(
                        'A-1': {
                            stage('A-1') {
                                echo "Doing work in A-1"
                                sleep 2
                            }
                        },
                        'A-2': {
                            stage('A-2') {
                                echo "Doing work in A-2"
                                sleep 2
                            }
                        }
                    )

                    echo "Finished Branch A"
                }
            },

            // Second top-level branch
            BranchB: {
                stage('Branch B') {
                    echo "Starting Branch B"

                    // inner parallel inside Branch B
                    parallel(
                        'B-1': {
                            stage('B-1') {
                                echo "Doing work in B-1"
                                sleep 2
                            }
                        },
                        'B-2': {
                            stage('B-2') {
                                echo "Doing work in B-2"
                                sleep 2
                            }
                        }
                    )

                    echo "Finished Branch B"
                }
            }
        )
    }
}

with blue ocean:

with pipeline graph view:

Upstream changes

No response

Are you interested in contributing this feature?

No response