feat(api): implement file deletion (#2960)

This implements the file delete to the Django API. Previously, the code was only manipulating the database while leaving the file in place.

Co-authored-by: jo <ljonas@riseup.net>

api/libretime_api/schedule/models/schedule.py

@@ -1,4 +1,5 @@
 from django.db import models
+from django.utils.timezone import now
 
 
 class Schedule(models.Model):
@@ -115,6 +116,14 @@ class Schedule(models.Model):
             return self.instance.ends_at
         return self.ends_at
 
+    @staticmethod
+    def is_file_scheduled_in_the_future(file_id):
+        count = Schedule.objects.filter(
+            file_id=file_id,
+            ends_at__gt=now(),
+        ).count()
+        return count > 0
+
     class Meta:
         managed = False
         db_table = "cc_schedule"