flows: add diagrams (#415)

* flows: initial diagram implementation

* web: install flowchart.js, add flow diagram page

* web: adjust diagram colours for dark mode

* flows: add permission checks for diagram

* flows: fix formatting

* web: fix formatting for web

* flows: add fix when last stage has policy

* flows: add test for diagram

* web: flows/diagram: add support for light mode

* flows: make Flows's Diagram API return json, add more tests and fix swagger response

web/src/api/Flows.ts

@@ -30,6 +30,10 @@ export class Flow {
         return DefaultClient.fetch<Flow>(["flows", "instances", slug]);
     }
 
+    static diagram(slug: string): Promise<{ diagram: string }> {
+        return DefaultClient.fetch<{ diagram: string }>(["flows", "instances", slug, "diagram"]);
+    }
+
     static list(filter?: QueryArguments): Promise<PBResponse<Flow>> {
         return DefaultClient.fetch<PBResponse<Flow>>(["flows", "instances"], filter);
     }