Added button to sandbox to launch `null_dag` capability

apps/web/src/app/workspaces/workspaces.component.html

@@ -31,6 +31,16 @@
         Launch null at NMT
       </button>
     </div>
+    <div class="d-flex px-2">
+      <button
+        type="button"
+        id="launchNullDagCapability"
+        class="btn btn-secondary btn-lg"
+        (click)="nullDagButtonOnClick()"
+      >
+        Launch multi-stage null capability
+      </button>
+    </div>
   </div>
 </div>
 <div class="container border rounded py-3 my-3">

apps/web/src/app/workspaces/workspaces.component.ts

 import { Component, OnInit } from "@angular/core";
 import { CapabilityLauncherService } from "./services/capability-launcher.service";
 import { CapabilityRequest } from "./model/capability-request";
-import { CapabilityExecution } from "./model/capability-execution";
 import { JsonObject } from "@angular/compiler-cli/ngcc/src/packages/entry_point";
-import { ActivatedRoute, Router } from "@angular/router";
 import { CapabilityRequestService } from "./services/capability-request.service";
 
 @Component({
@@ -51,6 +49,13 @@ export class WorkspacesComponent implements OnInit {
     this.launchCapability("null", { arguments: "-g", remote: true });
   }
 
+  /**
+   * OnClick method that creates a capability request for the null_dag capability
+   */
+  nullDagButtonOnClick(): void {
+    this.launchCapability("null_dag", {});
+  }
+
   /**
    * OnClick method that creates a capability request a given capability and submits it with the standard parameters:
    * - Product locator