Fix schedule event not supported on ADO (#12013)

* Add support for schedule event

* Add supported event for signify-prod

* Verify existence of GITHUB_SHA and GITHUB_REF for wofklow_disptach and schedule events.

* Add explanation in comment

* Fix linter issues

* Add scheudle to ADO supported events

pkg/azuredevops/pipelines/templatesParams.go

@@ -9,7 +9,7 @@ import (
 	"strconv"
 )
 
-var validJobTypes = []string{"presubmit", "postsubmit", "workflow_dispatch"}
+var validJobTypes = []string{"presubmit", "postsubmit", "workflow_dispatch", "schedule"}
 
 func GetValidJobTypes() []string {
 	return validJobTypes