Downloadable artifacts: make PDF and ePub opt-in by default (#10115)

Newly created projects will have PDF and ePub disabled by default. This matches
the default value of `formats` in the YAML file v2.

Building PDF and ePub is not a trivial task and many projects start failing
because of this or, if succeeding, they are just building pretty low quality PDF
and ePub files --which is a waste of resources.

This commit disables this by default for new projects, keeping the old projects
working as they are currently.

readthedocs/projects/migrations/0098_pdf_epub_opt_in.py

@@ -0,0 +1,49 @@
+# Generated by Django 3.2.18 on 2023-03-06 20:08
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("projects", "0097_add_http_header"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="historicalproject",
+            name="enable_epub_build",
+            field=models.BooleanField(
+                default=False,
+                help_text="Create a EPUB version of your documentation with each build.",
+                verbose_name="Enable EPUB build",
+            ),
+        ),
+        migrations.AlterField(
+            model_name="historicalproject",
+            name="enable_pdf_build",
+            field=models.BooleanField(
+                default=False,
+                help_text="Create a PDF version of your documentation with each build.",
+                verbose_name="Enable PDF build",
+            ),
+        ),
+        migrations.AlterField(
+            model_name="project",
+            name="enable_epub_build",
+            field=models.BooleanField(
+                default=False,
+                help_text="Create a EPUB version of your documentation with each build.",
+                verbose_name="Enable EPUB build",
+            ),
+        ),
+        migrations.AlterField(
+            model_name="project",
+            name="enable_pdf_build",
+            field=models.BooleanField(
+                default=False,
+                help_text="Create a PDF version of your documentation with each build.",
+                verbose_name="Enable PDF build",
+            ),
+        ),
+    ]

readthedocs/projects/models.py

@@ -324,14 +324,14 @@ class Project(models.Model):
     # Sphinx specific build options.
     enable_epub_build = models.BooleanField(
         _('Enable EPUB build'),
-        default=True,
+        default=False,
         help_text=_(
             'Create a EPUB version of your documentation with each build.',
         ),
     )
     enable_pdf_build = models.BooleanField(
         _('Enable PDF build'),
-        default=True,
+        default=False,
         help_text=_(
             'Create a PDF version of your documentation with each build.',
         ),