(core) Adds endpoint to update webhook

Summary:
Adds a new endpoint to update webhook.

Perform some refactoring to allow code reuse from endpoint allowing to _subscribe and _unsubscribe webhooks.

One aspect of webhook is that url are stored in the home db while the rest of the fields (tableRef, isReadyColRef, ...) are stored in sqlite. So care must be taken when updating fields, to properly rollback if anything should fail.

Follow up diff will bring UI to edit webhook list

Test Plan: Updated doc api server tests

Reviewers: jarek

Reviewed By: jarek

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D3821

app/common/Triggers.ts

@@ -0,0 +1,32 @@
+export interface WebhookFields {
+  url: string;
+  eventTypes: Array<"add"|"update">;
+  tableId: string;
+  enabled?: boolean;
+  isReadyColumn?: string|null;
+}
+
+// WebhookSubscribe should be `Omit<WebhookFields, 'tableId'>` (because subscribe endpoint read
+// tableId from the url) but generics are not yet supported by ts-interface-builder
+export interface WebhookSubscribe {
+  url: string;
+  eventTypes: Array<"add"|"update">;
+  enabled?: boolean;
+  isReadyColumn?: string|null;
+}
+
+// Describes fields to update a webhook
+export interface WebhookUpdate {
+  id: string;
+  fields: WebhookPatch;
+}
+
+// WebhookPatch should be `Partial<WebhookFields>` but generics are not yet supported by
+// ts-interface-builder
+export interface WebhookPatch {
+  url?: string;
+  eventTypes?: Array<"add"|"update">;
+  tableId?: string;
+  enabled?: boolean;
+  isReadyColumn?: string|null;
+}