✨(models/api) add link access reach and role

Link access was either public or private and was only allowing readers.

This commit makes link access more powerful:
- link reach can be private (users need to obtain specific access by
  document's administrators), restricted (any authenticated user) or
  public (anybody including anonymous users)
- link role can be reader or editor.

It is thus now possible to give editor access to an anonymous user or
any authenticated user.

src/backend/core/migrations/0003_document_link_reach_document_link_role_and_more.py

@@ -0,0 +1,52 @@
+# Generated by Django 5.1 on 2024-09-08 16:55
+
+import django.db.models.deletion
+import uuid
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0002_create_pg_trgm_extension'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='document',
+            name='link_reach',
+            field=models.CharField(choices=[('restricted', 'Restricted'), ('authenticated', 'Authenticated'), ('public', 'Public')], default='authenticated', max_length=20),
+        ),
+        migrations.AddField(
+            model_name='document',
+            name='link_role',
+            field=models.CharField(choices=[('reader', 'Reader'), ('editor', 'Editor')], default='reader', max_length=20),
+        ),
+        migrations.AlterField(
+            model_name='document',
+            name='is_public',
+            field=models.BooleanField(null=True),
+        ),
+        migrations.AlterField(
+            model_name='user',
+            name='language',
+            field=models.CharField(choices="(('en-us', 'English'), ('fr-fr', 'French'))", default='en-us', help_text='The language in which the user wants to see the interface.', max_length=10, verbose_name='language'),
+        ),
+        migrations.CreateModel(
+            name='LinkTrace',
+            fields=[
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, help_text='primary key for the record as UUID', primary_key=True, serialize=False, verbose_name='id')),
+                ('created_at', models.DateTimeField(auto_now_add=True, help_text='date and time at which a record was created', verbose_name='created on')),
+                ('updated_at', models.DateTimeField(auto_now=True, help_text='date and time at which a record was last updated', verbose_name='updated on')),
+                ('document', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='link_traces', to='core.document')),
+                ('user', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='link_traces', to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'verbose_name': 'Document/user link trace',
+                'verbose_name_plural': 'Document/user link traces',
+                'db_table': 'impress_link_trace',
+                'constraints': [models.UniqueConstraint(fields=('user', 'document'), name='unique_link_trace_document_user', violation_error_message='A link trace already exists for this document/user.')],
+            },
+        ),
+    ]

src/backend/core/migrations/0004_migrate_is_public_to_link_reach.py

@@ -0,0 +1,35 @@
+# Generated by Django 5.1 on 2024-09-08 17:04
+from django.db import migrations
+
+def migrate_is_public_to_link_reach(apps, schema_editor):
+    """
+    Forward migration: Migrate 'is_public' to 'link_reach'.
+    If is_public == True, set link_reach to 'public'
+    """
+    Document = apps.get_model('core', 'Document')
+    Document.objects.filter(is_public=True).update(link_reach='public')
+
+
+def reverse_migrate_link_reach_to_is_public(apps, schema_editor):
+    """
+    Reverse migration: Migrate 'link_reach' back to 'is_public'.
+    - If link_reach == 'public', set is_public to True
+    - Else set is_public to False
+    """
+    Document = apps.get_model('core', 'Document')
+    Document.objects.filter(link_reach='public').update(is_public=True)
+    Document.objects.filter(link_reach__in=['restricted', "authenticated"]).update(is_public=False)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0003_document_link_reach_document_link_role_and_more'),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            migrate_is_public_to_link_reach, 
+            reverse_migrate_link_reach_to_is_public
+        ),
+    ]