Consider adding Max Execution time in MySQL Data Source

Originally posted by @PeterZaitsev February 24, 2019 in discussion https://github.com/grafana/grafana/discussions/37005 In Dashboards it is easy to accidentally trigger query which will take too long time to complete potentially overloading host. I would suggest adding option to set maximum execution time for queries which could b configured as part of data source. it can be done by setting max_execution_time session variable If you want it more generic you can allow to specify commands which will be ran at data source initialization which can set this or other custom variables</div>