changelog: add notes about closing #11711

[skip ci]

CHANGELOG.md

 # 5.4.0 (unreleased)
 
+### New Features
+
+* **Postgres/MySQL/MSSQL**: Adds support for configuration of max open/idle connections and connection max lifetime. Also, panels with multiple SQL queries will now be executed concurrently [#11711](https://github.com/grafana/grafana/issues/11711), thx [@connection-reset](https://github.com/connection-reset)
+
 ### Minor
 
 * **Datasource Proxy**: Keep trailing slash for datasource proxy requests [#13326](https://github.com/grafana/grafana/pull/13326), thx [@ryantxu](https://github.com/ryantxu)
 
+### Breaking changes
+
+* Postgres/MySQL/MSSQL datasources now per default uses `max open connections` = `unlimited` (earlier 10), `max idle connections` = `2` (earlier 10) and `connection max lifetime` = `4` hours (earlier unlimited)
+
 # 5.3.0 (2018-10-10)
 
 * **Stackdriver**: Filter wildcards and regex matching are not yet supported [#13495](https://github.com/grafana/grafana/issues/13495)