(core) Add authSubject and authProvider to sessions

Summary:
This also updates Authorizer to link the authSubject
to Grist users if not previously linked. Linked subjects
are now used as the username for password-based logins,
instead of emails, which remain as a fallback.

Test Plan: Existing tests, and tested login flows manually.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3356

test/nbrowser/gristUtils.ts

@@ -1760,10 +1760,8 @@ export async function addSupportUserIfPossible() {
   if (!server.isExternalServer() && process.env.TEST_SUPPORT_API_KEY) {
     // Make sure we have a test support user.
     const dbManager = await server.getDatabase();
-    const user = await dbManager.getUserByLoginWithRetry('support@getgrist.com', {
-      email: 'support@getgrist.com',
-      name: 'Support',
-    });
+    const profile = {email: 'support@getgrist.com', name: 'Support'};
+    const user = await dbManager.getUserByLoginWithRetry('support@getgrist.com', {profile});
     if (!user) {
       throw new Error('Failed to create test support user');
     }