Provisioning: Allows specifying uid for datasource and use that in derived fields (#23585)

* Add uid to datasource

* Fix uid passing when provisioning

* Better error handling and Uid column type change

* Fix test and strict null error counts

* Add backend tests

* Add tests

* Fix strict null checks

* Update test

* Improve tests

* Update pkg/services/sqlstore/datasource.go

Co-Authored-By: Arve Knudsen <arve.knudsen@gmail.com>

* Variable rename

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

pkg/api/frontendsettings.go

@@ -67,6 +67,7 @@ func (hs *HTTPServer) getFrontendSettingsMap(c *models.ReqContext) (map[string]i
 
 		var dsMap = map[string]interface{}{
 			"id":   ds.Id,
+			"uid":  ds.Uid,
 			"type": ds.Type,
 			"name": ds.Name,
 			"url":  url,