Postgres/MySQL/MSSQL: Adds support for region annotations (#20752)

Adds support for region annotations in Postgres, MySQL and 
MSSQL data sources by adding a column named timeend to 
annotation query.

Co-Authored-By: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

Closes #20918
Ref #10589

pkg/tsdb/sqleng/sql_engine.go

@@ -56,6 +56,8 @@ var NewXormEngine = func(driverName string, connectionString string) (*xorm.Engi
 	return xorm.NewEngine(driverName, connectionString)
 }
 
+const timeEndColumnName = "timeend"
+
 type sqlQueryEndpoint struct {
 	macroEngine            SqlMacroEngine
 	queryResultTransformer SqlQueryResultTransformer
@@ -218,6 +220,7 @@ func (e *sqlQueryEndpoint) transformToTable(query *tsdb.Query, rows *core.Rows,
 
 	rowCount := 0
 	timeIndex := -1
+	timeEndIndex := -1
 
 	table := &tsdb.Table{
 		Columns: make([]tsdb.TableColumn, columnCount),
@@ -232,6 +235,11 @@ func (e *sqlQueryEndpoint) transformToTable(query *tsdb.Query, rows *core.Rows,
 				timeIndex = i
 				break
 			}
+
+			if timeIndex >= 0 && name == timeEndColumnName {
+				timeEndIndex = i
+				break
+			}
 		}
 	}
 
@@ -250,10 +258,11 @@ func (e *sqlQueryEndpoint) transformToTable(query *tsdb.Query, rows *core.Rows,
 			return err
 		}
 
-		// converts column named time to unix timestamp in milliseconds
+		// converts column named time and timeend to unix timestamp in milliseconds
 		// to make native mssql datetime types and epoch dates work in
 		// annotation and table queries.
 		ConvertSqlTimeColumnToEpochMs(values, timeIndex)
+		ConvertSqlTimeColumnToEpochMs(values, timeEndIndex)
 		table.Rows = append(table.Rows, values)
 	}