feat: add comment to export of availabilities

resolves #23

web/src/endpoints/export/get_availability_data.rs

@@ -39,6 +39,7 @@ struct ExportAvailabillity {
     start_time: NaiveTime,
     end_time: NaiveTime,
     assigned: bool,
+    comment: String
 }
 
 #[actix_web::get("/export/availabilitydata")]
@@ -86,6 +87,7 @@ pub async fn get(
                 start_time,
                 end_time,
                 assigned: false,
+                comment: a.comment.unwrap_or(String::new())
             }
         })
         .collect();