Make search model configurable on server

- Expose ability to modify search model via Django admin interface
- Previously the bi_encoder and cross_encoder models to use were set
  in code
- Now it's user configurable but with a default config generated by
  default

src/database/migrations/0017_searchmodel.py

@@ -0,0 +1,32 @@
+# Generated by Django 4.2.5 on 2023-11-14 23:25
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("database", "0016_alter_subscription_renewal_date"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="SearchModel",
+            fields=[
+                ("id", models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name="ID")),
+                ("created_at", models.DateTimeField(auto_now_add=True)),
+                ("updated_at", models.DateTimeField(auto_now=True)),
+                ("name", models.CharField(default="default", max_length=200)),
+                ("model_type", models.CharField(choices=[("text", "Text")], default="text", max_length=200)),
+                ("bi_encoder", models.CharField(default="thenlper/gte-small", max_length=200)),
+                (
+                    "cross_encoder",
+                    models.CharField(
+                        blank=True, default="cross-encoder/ms-marco-MiniLM-L-6-v2", max_length=200, null=True
+                    ),
+                ),
+            ],
+            options={
+                "abstract": False,
+            },
+        ),
+    ]