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

docs/sources/features/datasources/mysql.md

@@ -182,7 +182,7 @@ The resulting table panel:
 
 ## Time series queries
 
-If you set `Format as` to `Time series`, for use in Graph panel for example, then the query must return a column named `time` that returns either a sql datetime or any numeric datatype representing Unix epoch.
+If you set `Format as` to `Time series`, for use in Graph panel for example, then the query must return a column named `time` that returns either a SQL datetime or any numeric datatype representing Unix epoch.
 Any column except `time` and `metric` is treated as a value column.
 You may return a column named `metric` that is used as metric name for the value column.
 If you return multiple value columns and a column named `metric` then this column is used as prefix for the series name (only available in Grafana 5.3+).
@@ -350,7 +350,7 @@ WHERE
   $__unixEpochFilter(epoch_time)
 ```
 
-**Example query using time column of native sql date/time data type:**
+**Example query using time column of native SQL date/time data type:**
 
 ```sql
 SELECT
@@ -365,7 +365,8 @@ WHERE
 
 Name | Description
 ------------ | -------------
-time | The name of the date/time field. Could be a column with a native sql date/time data type or epoch value.
+time | The name of the date/time field. Could be a column with a native SQL date/time data type or epoch value.
+timeend | Optional name of the end date/time field. Could be a column with a native SQL date/time data type or epoch value.
 text | Event description field.
 tags | Optional field name to use for event tags as a comma separated string.