(core) Adding new column in users table "ref" with unique identifier.

Summary:
There is a new column in users table called ref (user reference).
It holds user's unique reference number that can be used for features
that require some kind of ownership logic (like comments).

Test Plan: Updated tests

Reviewers: georgegevoian, paulfitz

Reviewed By: georgegevoian, paulfitz

Differential Revision: https://phab.getgrist.com/D3641

app/server/lib/GranularAccess.ts

@@ -1608,6 +1608,7 @@ export class GranularAccess implements GranularAccessForBundle {
     user.Origin = docSession.req?.get('origin') || null;
     user.SessionID = isAnonymous ? `a${getDocSessionAltSessionId(docSession)}` : `u${user.UserID}`;
     user.IsLoggedIn = !isAnonymous;
+    user.UserRef = fullUser?.ref || null; // Empty string should be treated as null.
 
     if (this._ruler.ruleCollection.ruleError && !this._recoveryMode) {
       // It is important to signal that the doc is in an unexpected state,
@@ -2600,6 +2601,7 @@ export class User implements UserInfo {
   public Origin: string | null = null;
   public LinkKey: Record<string, string | undefined> = {};
   public Email: string | null = null;
+  public UserRef: string | null = null;
   [attribute: string]: any;
 
   constructor(_info: Record<string, unknown> = {}) {