add a field date_last_msg_sent in ticket.sql install file

modify migration script

htdocs/install/mysql/migration/15.0.0-16.0.0.sql

@@ -87,6 +87,7 @@ INSERT INTO llx_c_action_trigger (code,label,description,elementtype,rang) value
 INSERT INTO llx_c_action_trigger (code,label,description,elementtype,rang) values ('EXPENSE_REPORT_MODIFY','Expense report modified','Executed when an expense report is modified','expensereport',202);
 INSERT INTO llx_c_action_trigger (code,label,description,elementtype,rang) values ('HOLIDAY_MODIFY','Expense report modified','Executed when an expense report is modified','expensereport',212);
 
+ALTER TABLE llx_ticket ADD COLUMN date_last_msg_sent datetime AFTER date_read;
 
 CREATE TABLE llx_stock_mouvement_extrafields (
     rowid integer AUTO_INCREMENT PRIMARY KEY,

htdocs/install/mysql/tables/llx_ticket.sql

@@ -36,6 +36,7 @@ CREATE TABLE llx_ticket
 	severity_code varchar(32),
 	datec datetime,
 	date_read datetime,
+	date_last_msg_sent datetime,
 	date_close datetime,
 	notify_tiers_at_create tinyint,
 	email_msgid varchar(255),				-- if ticket is created by email collector, we store here MSG ID