feat: add series for builds table

this new field will help to search builds by series instead of
compiler, config_name, and arch.

It must be a MD5 field concatenating these three fields. We will
generate it automatically though generated column in the DB.

closes #1474 and part of #1454

Author: LucasSantos27

backend/kernelCI_app/migrations/0003_add_build_series_field.py

@@ -0,0 +1,33 @@
+# Generated by Django 5.1.10 on 2025-09-10 16:52
+
+import django.db.models.functions.text
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("kernelCI_app", "0002_remove_fk_constraint"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="builds",
+            name="series",
+            field=models.GeneratedField(
+                db_persist=True,
+                expression=django.db.models.functions.text.MD5(
+                    django.db.models.functions.text.Concat(
+                        models.F("config_name"),
+                        models.F("compiler"),
+                        models.F("architecture"),
+                    )
+                ),
+                output_field=models.TextField(blank=True, null=True),
+            ),
+        ),
+        migrations.AddIndex(
+            model_name="builds",
+            index=models.Index(fields=["series"], name="builds_series_idx"),
+        ),
+    ]

backend/kernelCI_app/models.py

@@ -1,5 +1,7 @@
 from django.db import models
 from django.contrib.postgres.fields import ArrayField
+from django.db.models import F
+from django.db.models.functions import Concat, MD5
 
 
 class StatusChoices(models.TextChoices):
@@ -87,9 +89,23 @@ class Builds(models.Model):
     status = models.CharField(
         max_length=10, choices=StatusChoices.choices, blank=True, null=True
     )
+    series = models.GeneratedField(
+        expression=MD5(
+            Concat(
+                F("config_name"),
+                F("compiler"),
+                F("architecture"),
+            ),
+        ),
+        output_field=models.TextField(blank=True, null=True),
+        db_persist=True,
+    )
 
     class Meta:
         db_table = "builds"
+        indexes = [
+            models.Index(fields=["series"], name="builds_series_idx"),
+        ]
 
 
 class Tests(models.Model):