Multiple queue, multiple cluster in one site (#71)

* Support for multi-queue, multi-cluster configuration. API changes include:
  * Adding `cluster` to async_task() parameters and Task model
  * Adding argument --name to qcluster command
  * Necessary adjustments to Conf and Broker classes
  * Some admin improvements

* Add settings.Q_CLUSTER['ALT_CLUSTERS']: q_cluster config overrides for alternative clusters;
Add Conf.CLUSTER_NAME: separate usage from Conf.PREFIX;
QueueAdmin/OrmQ detail page enhanced: now displaying args/kwargs/q_options instead of encrypted payload.

* if `cluster` argument is not set (the default), async_task() and schedule() will be handled by the default cluster; Documentation update.

* Text cleanup

* Documentation update.

* Fix TIMEOUT setting in Windows for non-default cluster

---------

Co-authored-by: Stan Triepels <1939656+GDay@users.noreply.github.com>

django_q/migrations/0017_task_cluster_alter.py

@@ -0,0 +1,43 @@
+# Generated by Django 4.1.5 on 2023-03-07 12:18
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("django_q", "0016_schedule_intended_date_kwarg"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="task",
+            name="cluster",
+            field=models.CharField(blank=True, default=None, max_length=100, null=True),
+        ),
+        migrations.AlterField(
+            model_name="ormq",
+            name="key",
+            field=models.CharField(
+                help_text="Name of the target cluster", max_length=100
+            ),
+        ),
+        migrations.AlterField(
+            model_name="ormq",
+            name="lock",
+            field=models.DateTimeField(
+                help_text="Prevent any cluster from pulling until", null=True
+            ),
+        ),
+        migrations.AlterField(
+            model_name="schedule",
+            name="cluster",
+            field=models.CharField(
+                blank=True,
+                default=None,
+                help_text="Name of the target cluster",
+                max_length=100,
+                null=True,
+            ),
+        ),
+    ]