(core) Enforce daily limit on API usage

Summary:
Keep track of the number of API requests made for this document today in redis. Uses local caches of the count and the document so that usually requests can proceed without waiting for redis or the database.

Moved the free standing function apiThrottle to become a method to avoid adding another layer of request handler callbacks.

Test Plan: Added a DocApi test

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: dsagal

Differential Revision: https://phab.getgrist.com/D3327

stubs/app/server/declarations.d.ts

@@ -71,5 +71,7 @@ declare module "redis" {
     public srem(key: string, val: string): Multi;
     public rpush(key: string, ...vals: string[]): Multi;
     public ltrim(key: string, start: number, end: number): Multi;
+    public incr(key: string): Multi;
+    public expire(key: string, seconds: number): Multi;
   }
 }