add start_time to build table

docs/schema-update-cgen.sql

@@ -45,6 +45,7 @@ CREATE INDEX image_listing_archives on image_archive_listing(archive_id);
 -- new columns --
 
 select statement_timestamp(), 'Adding new columns' as msg;
+ALTER TABLE build ADD COLUMN start_time TIMESTAMP;
 ALTER TABLE build ADD COLUMN extra TEXT;
 ALTER TABLE rpminfo ADD COLUMN extra TEXT;
 ALTER TABLE archiveinfo ADD COLUMN extra TEXT;

docs/schema.sql

@@ -290,6 +290,7 @@ CREATE TABLE build (
 	release TEXT NOT NULL,
 	epoch INTEGER,
 	create_event INTEGER NOT NULL REFERENCES events(id) DEFAULT get_event(),
+	start_time TIMESTAMP,
 	completion_time TIMESTAMP,
 	state INTEGER NOT NULL,
 	task_id INTEGER REFERENCES task (id),