Adddons: allow injecting an "always live" JavaScript file (#11758)

We talked about giving users a way to inject a JavaScript file they
control using our Cloudflare Worker infrastructure to allow them
manipulate frozen documentations.

This could be used in different ways to fix bugs or add features to a
particular frozen set of docs or even to all the versions. The user can
make usage of API data to filter by version or not
(e.g. `if (versions.current == "v3.0") { .. do something ...} `)

The script could live in Read the Docs itself using a relative URL, or
outside it, using an absolute URL.


### Example using Sphinx

1. [Tell Sphinx to include `static`
folder](https://github.com/readthedocs/test-builds/blob/full-feature/docs/conf.py#L25)
2. [Include a `readthedocs.js` file in your
project](https://github.com/readthedocs/test-builds/blob/full-feature/docs/static/readthedocs.js)
3. Make `AddonsConfig.userjsfile_src` to be
`/en/full-feature/readthedocs.js` from addons admin UX

The console will render the following:


![Screenshot_2024-11-11_18-13-59](https://github.com/user-attachments/assets/9fa46525-3b20-4d88-9950-f0a93a1199ab)

Related #11474
Related readthedocs/addons#431

readthedocs/projects/migrations/0135_addons_customscript.py

@@ -0,0 +1,35 @@
+# Generated by Django 4.2.16 on 2024-11-13 13:34
+
+from django.db import migrations, models
+from django_safemigrate import Safe
+
+
+class Migration(migrations.Migration):
+    safe = Safe.before_deploy
+
+    dependencies = [
+        ('projects', '0134_addons_load_when_embedded_notnull'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='addonsconfig',
+            name='customscript_enabled',
+            field=models.BooleanField(default=False, null=True),
+        ),
+        migrations.AddField(
+            model_name='addonsconfig',
+            name='customscript_src',
+            field=models.CharField(blank=True, help_text='URL to a JavaScript file to inject at serve time', max_length=512, null=True),
+        ),
+        migrations.AddField(
+            model_name='historicaladdonsconfig',
+            name='customscript_enabled',
+            field=models.BooleanField(default=False, null=True),
+        ),
+        migrations.AddField(
+            model_name='historicaladdonsconfig',
+            name='customscript_src',
+            field=models.CharField(blank=True, help_text='URL to a JavaScript file to inject at serve time', max_length=512, null=True),
+        ),
+    ]

readthedocs/projects/migrations/0136_addons_customscript_notnull.py

@@ -0,0 +1,25 @@
+# Generated by Django 4.2.16 on 2024-11-13 13:36
+
+from django.db import migrations, models
+from django_safemigrate import Safe
+
+
+class Migration(migrations.Migration):
+    safe = Safe.after_deploy
+
+    dependencies = [
+        ('projects', '0135_addons_customscript'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='addonsconfig',
+            name='customscript_enabled',
+            field=models.BooleanField(default=False),
+        ),
+        migrations.AlterField(
+            model_name='historicaladdonsconfig',
+            name='customscript_enabled',
+            field=models.BooleanField(default=False),
+        ),
+    ]

readthedocs/projects/models.py

@@ -222,6 +222,18 @@ class AddonsConfig(TimeStampedModel):
     search_enabled = models.BooleanField(default=True)
     search_default_filter = models.CharField(null=True, blank=True, max_length=128)
 
+    # User JavaScript File
+    customscript_enabled = models.BooleanField(default=False)
+
+    # This is a user-defined file that will be injected at serve time by our
+    # Cloudflare Worker if defined
+    customscript_src = models.CharField(
+        max_length=512,
+        null=True,
+        blank=True,
+        help_text="URL to a JavaScript file to inject at serve time",
+    )
+
     # Notifications
     notifications_enabled = models.BooleanField(default=True)
     notifications_show_on_latest = models.BooleanField(default=True)

readthedocs/proxito/tests/responses/v1.json

@@ -164,6 +164,10 @@
       "default_filter": "project:project/latest",
       "filters": []
     },
+    "customscript": {
+      "enabled": false,
+      "src": null
+    },
     "linkpreviews": {
       "enabled": false,
       "root_selector": "[role=main] a.internal",

readthedocs/proxito/views/hosting.py

@@ -490,6 +490,10 @@ def _v1(self, project, version, build, filename, url, request):
                     #     "filepath": "/docs/index.rst",
                     # },
                 },
+                "customscript": {
+                    "enabled": project.addons.customscript_enabled,
+                    "src": project.addons.customscript_src,
+                },
                 "search": {
                     "enabled": project.addons.search_enabled,
                     # TODO: figure it out where this data comes from.