record task duration in seconds

sql/pgsql/schema.sql

@@ -398,6 +398,7 @@ create table ttrss_error_log(
 create table ttrss_scheduled_tasks(
 	id serial not null primary key,
    task_name varchar(250) unique not null,
+   last_duration integer not null,
    last_rc integer not null,
    last_run timestamp not null default NOW());