NEW: Unlock all tasks via change list object tool link

for #102

Looks like:

![image](https://user-images.githubusercontent.com/71315/171357776-9fc55010-e86f-406a-85bf-eff055302ba5.png)

huey_monitor/admin.py

@@ -1,9 +1,12 @@
 from bx_django_utils.templatetags.humanize_time import human_duration
-from django.contrib import admin
+from django.contrib import admin, messages
 from django.contrib.admin.views.main import ChangeList
+from django.shortcuts import redirect
 from django.template.loader import render_to_string
+from django.urls import path, reverse
 from django.utils import timezone
 from django.utils.translation import gettext_lazy as _
+from huey.contrib.djhuey import HUEY
 
 from huey_monitor.models import SignalInfoModel, TaskModel
 
@@ -78,6 +81,29 @@ def duration(self, obj):
 
         return human_duration(obj.create_dt, end_dt)
 
+    def changelist_url(self):
+        info = (self.admin_site.name, self.model._meta.app_label, self.model._meta.model_name)
+        url_name = '%s:%s_%s_changelist' % info
+        return reverse(url_name, current_app=self.admin_site.name)
+
+    def flush_locks_view(self, request):
+        flushed = HUEY.flush_locks()
+        if not flushed:
+            messages.info(request, 'No tasks locks exists, nothing to flush, ok.')
+        else:
+            messages.success(request, f'Flush task locks: {", ".join(sorted(flushed))}')
+        return redirect(self.changelist_url())
+
+    def get_urls(self):
+        urls = [
+            path(
+                'flush_locks/',
+                self.admin_site.admin_view(self.flush_locks_view),
+                name='flush_locks',
+            ),
+        ] + super().get_urls()
+        return urls
+
     list_display = (
         'human_update_dt',
         'column_name',

huey_monitor/templates/admin/huey_monitor/taskmodel/change_list_object_tools.html

@@ -0,0 +1,13 @@
+{% extends "admin/change_form_object_tools.html" %}
+{% load i18n admin_urls %}
+
+{% block object-tools-items %}
+  {% if has_add_permission %}
+  <li>
+    <a href="{% url 'admin:flush_locks' %}">
+      {% trans 'Flush all task locks' %}
+    </a>
+  </li>
+  {% endif %}
+  {{ block.super }}
+{% endblock %}

huey_monitor_tests/tests/test_huey_monitor.py

@@ -98,3 +98,18 @@ def test_raise_error_task(self):
             'Traceback (most recent call last):',
             'AssertionError: This is a test exception',
         ))
+
+    def test_admin_flush_locks_view(self):
+        flush_locks_url = '/admin/huey_monitor/taskmodel/flush_locks/'
+        response = self.client.get(flush_locks_url)
+        self.assertRedirects(
+            response, expected_url='/admin/login/?next=/admin/huey_monitor/taskmodel/flush_locks/'
+        )
+        self.assert_messages(response, expected_messages=[])
+
+        self.client.force_login(self.superuser)
+        response = self.client.get(flush_locks_url)
+        self.assertRedirects(response, expected_url='/admin/huey_monitor/taskmodel/')
+        self.assert_messages(
+            response, expected_messages=['No tasks locks exists, nothing to flush, ok.']
+        )