(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/Triggers-ti.ts

@@ -10,13 +10,36 @@ export const WebhookFields = t.iface([], {
   "tableId": "string",
   "enabled": t.opt("boolean"),
   "isReadyColumn": t.opt(t.union("string", "null")),
+  "name": t.opt("string"),
+  "memo": t.opt("string"),
 });
 
+export const WebhookBatchStatus = t.union(t.lit('success'), t.lit('failure'), t.lit('rejected'));
+
+export const WebhookStatus = t.union(t.lit('idle'), t.lit('sending'), t.lit('retrying'), t.lit('postponed'), t.lit('error'), t.lit('invalid'));
+
 export const WebhookSubscribe = t.iface([], {
   "url": "string",
   "eventTypes": t.array(t.union(t.lit("add"), t.lit("update"))),
   "enabled": t.opt("boolean"),
   "isReadyColumn": t.opt(t.union("string", "null")),
+  "name": t.opt("string"),
+  "memo": t.opt("string"),
+});
+
+export const WebhookSummary = t.iface([], {
+  "id": "string",
+  "fields": t.iface([], {
+    "url": "string",
+    "unsubscribeKey": "string",
+    "eventTypes": t.array("string"),
+    "isReadyColumn": t.union("string", "null"),
+    "tableId": "string",
+    "enabled": "boolean",
+    "name": "string",
+    "memo": "string",
+  }),
+  "usage": t.union("WebhookUsage", "null"),
 });
 
 export const WebhookUpdate = t.iface([], {
@@ -30,12 +53,39 @@ export const WebhookPatch = t.iface([], {
   "tableId": t.opt("string"),
   "enabled": t.opt("boolean"),
   "isReadyColumn": t.opt(t.union("string", "null")),
+  "name": t.opt("string"),
+  "memo": t.opt("string"),
+});
+
+export const WebhookUsage = t.iface([], {
+  "numWaiting": "number",
+  "status": "WebhookStatus",
+  "updatedTime": t.opt(t.union("number", "null")),
+  "lastSuccessTime": t.opt(t.union("number", "null")),
+  "lastFailureTime": t.opt(t.union("number", "null")),
+  "lastErrorMessage": t.opt(t.union("string", "null")),
+  "lastHttpStatus": t.opt(t.union("number", "null")),
+  "lastEventBatch": t.opt(t.union("null", t.iface([], {
+    "size": "number",
+    "errorMessage": t.union("string", "null"),
+    "httpStatus": t.union("number", "null"),
+    "status": "WebhookBatchStatus",
+    "attempts": "number",
+  }))),
+  "numSuccess": t.opt(t.iface([], {
+    "pastHour": "number",
+    "past24Hours": "number",
+  })),
 });
 
 const exportedTypeSuite: t.ITypeSuite = {
   WebhookFields,
+  WebhookBatchStatus,
+  WebhookStatus,
   WebhookSubscribe,
+  WebhookSummary,
   WebhookUpdate,
   WebhookPatch,
+  WebhookUsage,
 };
 export default exportedTypeSuite;