[FIX] website_profile: prevent losing search params

Before this commit, the "rank by" parameter was deleted when a visitor
added a search criteria. This commit solves this problem.

Steps to reproduce the issue:
- Go to "/profile/users"
- Click on "Rank by" and select "This week"
- Search for a user (e.g. "admin")

=> The "rank by" parameter is lost and if you click on "This week"
again, the search (admin) will be lost.

task-3058239

closes odoo/odoo#105462

Signed-off-by: Benoit Socias (bso) <bso@odoo.com>

addons/website_profile/views/website_profile.xml

@@ -36,6 +36,7 @@
                                     </button>
                                 </span>
                                 <input type="text" class="form-control border-0 rounded-0 bg-transparent text-white" name="search" placeholder="Search users"/>
+                                <input type="hidden" name="group_by" t-att-value="group_by"/>
                             </div>
                         </form>
                     </div>