Change source title and siglum to optional

This is to allow saving sources in the create / edit without triggering a validation error.

django/cantusdb_project/main_app/migrations/0022_alter_source_siglum_alter_source_title.py

@@ -0,0 +1,32 @@
+# Generated by Django 4.1.6 on 2024-06-18 12:44
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("main_app", "0021_source_shelfmark"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="source",
+            name="siglum",
+            field=models.CharField(
+                blank=True,
+                help_text="RISM-style siglum + Shelf-mark (e.g. GB-Ob 202).",
+                max_length=63,
+                null=True,
+            ),
+        ),
+        migrations.AlterField(
+            model_name="source",
+            name="title",
+            field=models.CharField(
+                blank=True,
+                help_text="Full Source Identification (City, Archive, Shelf-mark)",
+                max_length=255,
+                null=True,
+            ),
+        ),
+    ]

django/cantusdb_project/main_app/models/source.py

@@ -27,14 +27,16 @@ class Source(BaseModel):
 
     title = models.CharField(
         max_length=255,
+        blank=True,
+        null=True,
         help_text="Full Source Identification (City, Archive, Shelf-mark)",
     )
     # the siglum field as implemented on the old Cantus is composed of both the RISM siglum and the shelfmark
     # it is a human-readable ID for a source
     siglum = models.CharField(
         max_length=63,
-        null=False,
-        blank=False,
+        null=True,
+        blank=True,
         help_text="RISM-style siglum + Shelf-mark (e.g. GB-Ob 202).",
     )
     holding_institution = models.ForeignKey(