(core) Adding /webhooks endpoint

Summary:
- New /webhooks event that lists all webhooks in a document (available for owners),
- Monitoring webhooks usage and saving it in memory or Redis,
- Loosening _usubscribe API endpoint, so that the information returned from the /webhook endpoint is enough to unsubscribe,
- Owners can remove webhook without the unsubscribe key.

The endpoint lists all webhooks that are registered in a document, not just webhooks from a single table.
There are two status fields. First for the webhook, second for the last request attempt.
Webhook can have 5 statuses: 'idle', 'sending', 'retrying', 'postponed', 'error', which roughly describes what the
sendLoop is currently doing. The 'error' status describes a situation when all request attempts failed and the queue needs
to be drained, so some requests were dropped.

The last request status can only be: 'success', 'failure' or 'rejected'. Rejected means that the last batch was dropped because the
queue was too long.

Test Plan: New and updated tests

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3727

app/gen-server/lib/DocApiForwarder.ts

@@ -56,6 +56,7 @@ export class DocApiForwarder {
     app.use('/api/docs/:docId/compare', withDoc);
     app.use('/api/docs/:docId/assign', withDocWithoutAuth);
     app.use('/api/docs/:docId/webhooks/queue', withDoc);
+    app.use('/api/docs/:docId/webhooks', withDoc);
     app.use('^/api/docs$', withoutDoc);
   }
 

app/gen-server/lib/HomeDBManager.ts

@@ -1807,18 +1807,23 @@ export class HomeDBManager extends EventEmitter {
     return secret?.value;
   }
 
-  public async removeWebhook(id: string, docId: string, unsubscribeKey: string): Promise<void> {
-    if (!(id && unsubscribeKey)) {
-      throw new ApiError('Bad request: id and unsubscribeKey both required', 400);
+  public async removeWebhook(id: string, docId: string, unsubscribeKey: string, checkKey: boolean): Promise<void> {
+    if (!id) {
+      throw new ApiError('Bad request: id required', 400);
+    }
+    if (!unsubscribeKey && checkKey) {
+      throw new ApiError('Bad request: unsubscribeKey required', 400);
     }
     return await this._connection.transaction(async manager => {
-      const secret = await this.getSecret(id, docId, manager);
-      if (!secret) {
-        throw new ApiError('Webhook with given id not found', 404);
-      }
-      const webhook = JSON.parse(secret) as WebHookSecret;
-      if (webhook.unsubscribeKey !== unsubscribeKey) {
-        throw new ApiError('Wrong unsubscribeKey', 401);
+      if (checkKey) {
+        const secret = await this.getSecret(id, docId, manager);
+        if (!secret) {
+          throw new ApiError('Webhook with given id not found', 404);
+        }
+        const webhook = JSON.parse(secret) as WebHookSecret;
+        if (webhook.unsubscribeKey !== unsubscribeKey) {
+          throw new ApiError('Wrong unsubscribeKey', 401);
+        }
       }
       await manager.createQueryBuilder()
         .delete()