(core) Adds a UI panel for managing webhooks

Summary:
This adds a UI panel for managing webhooks. Work started by Cyprien Pindat. You can find the UI on a document's settings page. Main changes relative to Cyprien's demo:

  * Changed behavior of virtual table to be more consistent with the rest of Grist, by factoring out part of the implementation of on-demand tables.
  * Cell values that would create an error can now be denied and reverted (as for the rest of Grist).
  * Changes made by other users are integrated in a sane way.
  * Basic undo/redo support is added using the regular undo/redo stack.
  * The table list in the drop-down is now updated if schema changes.
  * Added a notification from back-end when webhook status is updated so constant polling isn't needed to support multi-user operation.
  *  Factored out webhook specific logic from general virtual table support.
  * Made a bunch of fixes to various broken behavior.
  * Added tests.

The code remains somewhat unpolished, and behavior in the presence of errors is imperfect in general but may be adequate for this case.

I assume that we'll soon be lifting the restriction on the set of domains that are supported for webhooks - otherwise we'd want to provide some friendly way to discover that list of supported domains rather than just throwing an error.

I don't actually know a lot about how the front-end works - it looks like tables/columns/fields/sections can be safely added if they have string ids that won't collide with bone fide numeric ids from the back end. Sneaky.

Contains a migration, so needs an extra reviewer for that.

Test Plan: added tests

Reviewers: jarek, dsagal

Reviewed By: jarek, dsagal

Differential Revision: https://phab.getgrist.com/D3856

app/common/UserAPI.ts

@@ -14,7 +14,9 @@ import {OrgPrefs, UserOrgPrefs, UserPrefs} from 'app/common/Prefs';
 import * as roles from 'app/common/roles';
 import {addCurrentOrgToPath} from 'app/common/urlUtils';
 import {encodeQueryParams} from 'app/common/gutil';
-import {WebhookUpdate} from 'app/common/Triggers';
+import {WebhookFields, WebhookSubscribe, WebhookSummary, WebhookUpdate} from 'app/common/Triggers';
+import omitBy from 'lodash/omitBy';
+
 
 export type {FullUser, UserProfile};
 
@@ -454,8 +456,12 @@ export interface DocAPI {
   // Get users that are worth proposing to "View As" for access control purposes.
   getUsersForViewAs(): Promise<PermissionDataWithExtraUsers>;
 
+  getWebhooks(): Promise<WebhookSummary[]>;
+  addWebhook(webhook: WebhookFields): Promise<{webhookId: string}>;
+  removeWebhook(webhookId: string, tableId: string): Promise<void>;
   // Update webhook
   updateWebhook(webhook: WebhookUpdate): Promise<void>;
+  flushWebhooks(): Promise<void>;
 }
 
 // Operations that are supported by a doc worker.
@@ -905,6 +911,19 @@ export class DocAPIImpl extends BaseAPI implements DocAPI {
     return this.requestJson(`${this._url}/usersForViewAs`);
   }
 
+  public async getWebhooks(): Promise<WebhookSummary[]> {
+    return this.requestJson(`${this._url}/webhooks`);
+  }
+
+  public async addWebhook(webhook: WebhookSubscribe & {tableId: string}): Promise<{webhookId: string}> {
+    const {tableId} = webhook;
+    return this.requestJson(`${this._url}/tables/${tableId}/_subscribe`, {
+      method: 'POST',
+      body: JSON.stringify(
+        omitBy(webhook, (val, key) => key === 'tableId' || val === null)),
+    });
+  }
+
   public async updateWebhook(webhook: WebhookUpdate): Promise<void> {
     return this.requestJson(`${this._url}/webhooks/${webhook.id}`, {
       method: 'PATCH',
@@ -912,6 +931,21 @@ export class DocAPIImpl extends BaseAPI implements DocAPI {
     });
   }
 
+  public removeWebhook(webhookId: string, tableId: string) {
+    // unsubscribeKey is not required for owners
+    const unsubscribeKey = '';
+    return this.requestJson(`${this._url}/tables/${tableId}/_unsubscribe`, {
+      method: 'POST',
+      body: JSON.stringify({webhookId, unsubscribeKey}),
+    });
+  }
+
+  public async flushWebhooks(): Promise<void> {
+    await this.request(`${this._url}/webhooks/queue`, {
+      method: 'DELETE'
+    });
+  }
+
   public async forceReload(): Promise<void> {
     await this.request(`${this._url}/force-reload`, {
       method: 'POST'