Refactor regex for default Workflow URLs

Switch from static base pattern of `logic.azure.com` to a regex
OR pattern to permit either of `logic.azure.com` or
`*.azure-api.net` as has been observed in the wild.

This also has the side effect of resolving potential CodeQL
alerts raised in PR GH-275.

refs GH-262

send.go

@@ -36,7 +36,7 @@ const (
 
 // Known Workflow URL patterns for submitting messages to Microsoft Teams.
 const (
-	WorkflowURLBaseDomain = "logic.azure.com"
+	WorkflowURLBaseDomain = `^https:\/\/(?:.*)(:?\.azure-api|logic\.azure)\.(?:com|net)`
 )
 
 // DisableWebhookURLValidation is a special keyword used to indicate to