SQL Datasources: Update Max Connection and Max Idle Connection Defaults to 100 and add auto mode (#65834)

* Update connection configuration for SQL datasources

* Working auto state for connection numbers

* Add migration

* Use defaults from constants file

* Remove dead code

* Add tests and restructure useMigrateDatabaseField

* Update function names

* Update docs

* Make sure we don't continually issue updates

* Update docs

* Use onOptionsChnage in ConnectionLimits

* Update docs

* Clean up docs

* Update migration

* Fix default values in docs

* Fix spacing issue

* Fix test

* Update default values for SQL connections

* Include consts

* Allow override for default SQL datasource connection parameters

* Fix linter errors

* Remove extra @ts-ignore

* Centralize logic for default values

* Remove debugging

* Remove unecessary function

* Update configuration docs

* minor suggested change

* Fix comment misspelling

* Remove unecessary default setting code

* Update docs to indicate that code was included for backport version

* Remove dead code

---------

Co-authored-by: lwandz13 <larissa.wandzura@grafana.com>

pkg/tsdb/postgres/postgres.go

@@ -56,9 +56,9 @@ func (s *Service) newInstanceSettings(cfg *setting.Cfg) datasource.InstanceFacto
 	return func(settings backend.DataSourceInstanceSettings) (instancemgmt.Instance, error) {
 		logger.Debug("Creating Postgres query endpoint")
 		jsonData := sqleng.JsonData{
-			MaxOpenConns:        0,
-			MaxIdleConns:        2,
-			ConnMaxLifetime:     14400,
+			MaxOpenConns:        cfg.SqlDatasourceMaxOpenConnsDefault,
+			MaxIdleConns:        cfg.SqlDatasourceMaxIdleConnsDefault,
+			ConnMaxLifetime:     cfg.SqlDatasourceMaxConnLifetimeDefault,
 			Timescaledb:         false,
 			ConfigurationMethod: "file-path",
 			SecureDSProxy:       false,