Add graph model generator and update UI components

[AlanGreene]

Changes

#675

• add code to generate graph data model from set of Tekton resources
  representing a PipelineRun
• simplify graph model to remove unecessary fields
• add TaskRun / step status to nodes
• update UI components to support dynamically redrawing the diagram
• add click handlers so consumers can hook into graph interaction (Task / step
  selected)

Note: most of the diff (~600 lines) is sample data (examples/*.json) and can be ignored.

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[steveodonovan]

Should the three isSubGraph conditionals be in a single block outside the jsx ?

[AlanGreene]

what did you have in mind, something like this?

+let nodeOnClick = onClickTask;
+let nodeOnClickStep = onClickStep;
+let linkComponent = NodeLink;

+if (isSubGraph) {
+  nodeOnClick = onClickStep;
+  nodeOnClickStep = undefined;
+  linkComponent = () => null;
+}

...

  nodeComponent={c => (
    <Node
-      onClick={isSubGraph ? onClickStep : onClickTask}
+      onClick={nodeOnClick}
-      onClickStep={isSubGraph ? undefined : onClickStep}
+      onClickStep={nodeOnClickStep}
      {...c.node}
    />
  )}
-  linkComponent={isSubGraph ? () => null : NodeLink}
+  linkComponent={linkComponent}

not sure it's an improvement

[AlanGreene]

@steveodonovan thanks for the feedback, addressed it all bar the one still open above. Also refactored the main function in buildGraphData.js to extract the individual stages and hopefully make it a little more readable.

[steveodonovan]

/approve
/lgtm

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