SQL Datasources: Move database setting to jsonData (#58649)

* Datasource settings: Add deprecation notice for database field

* SQL Datasources: Migrate from settings.database to settings.jsonData.database

* Check jsonData first

* Remove comment from docs

pkg/tsdb/postgres/postgres.go

@@ -66,11 +66,17 @@ func (s *Service) newInstanceSettings(cfg *setting.Cfg) datasource.InstanceFacto
 		if err != nil {
 			return nil, fmt.Errorf("error reading settings: %w", err)
 		}
+
+		database := jsonData.Database
+		if database == "" {
+			database = settings.Database
+		}
+
 		dsInfo := sqleng.DataSourceInfo{
 			JsonData:                jsonData,
 			URL:                     settings.URL,
 			User:                    settings.User,
-			Database:                settings.Database,
+			Database:                database,
 			ID:                      settings.ID,
 			Updated:                 settings.Updated,
 			UID:                     settings.UID,