"Create forum post" button on a rig page (#551)

* Add button for creating forum thread draft from event detail

TODO: Allow RIGS to ingest POST requests sent from the forum on new posts in RIG info to link up the forum thread

RE https://forum.nottinghamtec.co.uk/t/rigs-discourse-integration/15592/21

* Mockup webhook recieving view

* Correct method of CRSF exemption for webhook reciever

* Use f-strings correctly, not like a big dumb

* That was also dumb, fix that too

* Second shot at webhook reciever

* Oops

* >.<

* Third shot

* Try again at signing

* What if I gave it the right arguments. That might be a good start.

* More fiddling with auth

* Add debug print

* Okay, put that back where it was because I inavertently overloaded my import

Flashbacks to my java days...

* Different header access method

* Fix import, again

* Fix ommited json parsing wotsit

* Fix url

* Fix string index

* Correct template logic

* Allow manual adding/editing of URLs

* Filter by right flavour of event

* Amend event str conversion for consistency

* Oops

* Make migration

Will be squashed later

* Fix logic when creating events

* Squash migration

* Implement codedoctor suggestion

RIGS/migrations/0050_event_forum_url.py

@@ -0,0 +1,19 @@
+# Generated by Django 3.2.19 on 2023-06-27 11:28
+
+import RIGS.models
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('RIGS', '0049_auto_20230529_1123'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='event',
+            name='forum_url',
+            field=models.URLField(blank=True, default='', validators=[RIGS.models.validate_forum_url]),
+        ),
+    ]