feat(workspaces): add thumbnail upload and lifecycle support

apps/workspaces/models.py

@@ -9,6 +9,7 @@ User = get_user_model()
 class Workspace(BaseModel):
     name = models.CharField(max_length=255)
     description = models.TextField(blank=True)
+    thumbnail = models.ImageField(upload_to="profile/workspaces/", blank=True, null=True)
     owner = models.ForeignKey(
         User,
         on_delete=models.PROTECT,