(core) set up a trialing list and a call scheduled flag for Grist SaaS

Summary:
This adds support for the automation described in
https://grist.quip.com/rt3tAoEH4kuy/Automate-Sprouts-outreach-email

Test Plan: added tests; will need manual testing and iterative integration work

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3804

app/gen-server/lib/HomeDBManager.ts

@@ -83,6 +83,8 @@ export const NotifierEvents = StringUnion(
   'addBillingManager',
   'teamCreator',
   'trialPeriodEndingSoon',
+  'trialingSubscription',
+  'scheduledCall',
 );
 
 export type NotifierEvent = typeof NotifierEvents.type;
@@ -467,6 +469,10 @@ export class HomeDBManager extends EventEmitter {
     return await User.findOne({where: {apiKey}, relations: ["logins"]}) || undefined;
   }
 
+  public async getUserByRef(ref: string): Promise<User|undefined> {
+    return await User.findOne({where: {ref}, relations: ["logins"]}) || undefined;
+  }
+
   public async getUser(userId: number): Promise<User|undefined> {
     return await User.findOne({where: {id: userId}, relations: ["logins"]}) || undefined;
   }