(core) Adding DELETE /api/docs/webhooks/queue endpoint to clear the queue

Summary:
Creating an API endpoint to cancel any queued webhook messages from
a document.

Test Plan: Updated

Reviewers: paulfitz, georgegevoian

Reviewed By: paulfitz, georgegevoian

Differential Revision: https://phab.getgrist.com/D3713

package.json

@@ -56,7 +56,7 @@
     "@types/mocha": "5.2.5",
     "@types/moment-timezone": "0.5.9",
     "@types/node": "^14",
-    "@types/node-fetch": "2.1.2",
+    "@types/node-fetch": "2.6.2",
     "@types/pidusage": "2.0.1",
     "@types/plotly.js": "2.12.1",
     "@types/qrcode": "1.4.2",
@@ -147,6 +147,7 @@
     "morgan": "1.9.1",
     "mousetrap": "1.6.2",
     "multiparty": "4.2.2",
+    "node-abort-controller": "3.0.1",
     "node-fetch": "2.6.7",
     "pg": "8.6.0",
     "plotly.js-basic-dist": "2.13.2",