WS-677: `null_dag` capability

Additions

• Added new capability: null_dag that simply launches the null_dag workflow
• Added button to launch new capability to the sandbox
• Changed "no-files" message to "No files are attached to this request."; added "no-parameters" message: "This request has no parameters."

Screenshot

New button

New empty-parameters/files messages

Completes WS-677 (for real this time)

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">