Add Website field to author

Authors have Websites. that might be interesting for BookWyrm users. Now there is a field specify the website of an author and it is shown tu users under the wikipedia link

Adds max char for ISFDB ID (6) and ISNI (19 - 16 plus three -)

bookwyrm/migrations/0173_auto_20221228_1436.py

@@ -0,0 +1,33 @@
+# Generated by Django 3.2.16 on 2022-12-28 14:36
+
+import bookwyrm.models.fields
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookwyrm", "0172_alter_user_preferred_language"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="author",
+            name="website",
+            field=bookwyrm.models.fields.CharField(
+                blank=True, max_length=255, null=True
+            ),
+        ),
+        migrations.AlterField(
+            model_name="author",
+            name="isfdb",
+            field=bookwyrm.models.fields.CharField(blank=True, max_length=6, null=True),
+        ),
+        migrations.AlterField(
+            model_name="author",
+            name="isni",
+            field=bookwyrm.models.fields.CharField(
+                blank=True, max_length=19, null=True
+            ),
+        ),
+    ]