(core) Add PUT /records DocApi endpoint to AddOrUpdate records

Summary:
As designed in https://grist.quip.com/fZSrAnJKgO5j/Add-or-Update-Records-API

Current `POST /records` adds records, and `PATCH /records` updates them by row ID. This adds `PUT /records` to 'upsert' records, applying the AddOrUpdate user action. PUT was chosen because it's idempotent. Using a separate method (instead of inferring based on the request body) also cleanly separates validation, documentation, etc.

The name `require` for the new property was suggested by Paul because `where` isn't very clear when adding records.

Test Plan: New DocApi tests

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3251

app/gen-server/lib/DocApiForwarder.ts

@@ -93,7 +93,7 @@ export class DocApiForwarder {
       method: req.method,
       headers,
     };
-    if (['POST', 'PATCH'].includes(req.method)) {
+    if (['POST', 'PATCH', 'PUT'].includes(req.method)) {
       // uses `req` as a stream
       options.body = req;
     }