Use BigInt for permissions field and remove max value validator

BigInt is needed as Discord's permissions number now exceeds that which can be stored
in a normal int. I have removed the max value validator, as this just adds
maintanence burden for us each time Discord adds new permissions.

pydis_site/apps/api/migrations/0070_auto_20210618_2114.py

@@ -0,0 +1,19 @@
+# Generated by Django 3.0.14 on 2021-06-18 21:14
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0069_documentationlink_validators'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='role',
+            name='permissions',
+            field=models.BigIntegerField(help_text='The integer value of the permission bitset of this role from Discord.', validators=[django.core.validators.MinValueValidator(limit_value=0, message='Role permissions cannot be negative.')]),
+        ),
+    ]

pydis_site/apps/api/models/bot/role.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from django.core.validators import MaxValueValidator, MinValueValidator
+from django.core.validators import MinValueValidator
 from django.db import models
 
 from pydis_site.apps.api.models.mixins import ModelReprMixin
@@ -38,16 +38,12 @@ class Role(ModelReprMixin, models.Model):
         ),
         help_text="The integer value of the colour of this role from Discord."
     )
-    permissions = models.IntegerField(
+    permissions = models.BigIntegerField(
         validators=(
             MinValueValidator(
                 limit_value=0,
                 message="Role permissions cannot be negative."
             ),
-            MaxValueValidator(
-                limit_value=2 << 32,
-                message="Role permission bitset exceeds value of having all permissions"
-            )
         ),
         help_text="The integer value of the permission bitset of this role from Discord."
     )