refactor: jellyfin authentication and add gravatar for missing avatars of jellyfin users (#664)

* refactor: jellyfin authentication

This refactor standardizes the authentication approach in Jellyfin to mirror the method employed in
Plex authentication for consistency

* feat: use gravatar for jellyfin users' with missing jellyfin avatars

server/routes/settings/index.ts

@@ -29,6 +29,7 @@ import { getAppVersion } from '@server/utils/appVersion';
 import { Router } from 'express';
 import rateLimit from 'express-rate-limit';
 import fs from 'fs';
+import gravatarUrl from 'gravatar-url';
 import { escapeRegExp, merge, omit, set, sortBy } from 'lodash';
 import { rescheduleJob } from 'node-schedule';
 import path from 'path';
@@ -337,7 +338,7 @@ settingsRoutes.get('/jellyfin/users', async (req, res) => {
     id: user.Id,
     thumb: user.PrimaryImageTag
       ? `${jellyfinHost}/Users/${user.Id}/Images/Primary/?tag=${user.PrimaryImageTag}&quality=90`
-      : '/os_logo_square.png',
+      : gravatarUrl(user.Name, { default: 'mm', size: 200 }),
     email: user.Name,
   }));