Changed ms custom meta tag

Changed ms custom meta tag to ms.custom: seo-azure-migrate for SEO keyword tracking purposes.

Author: JanetCThomas

articles/dms/index.yml

@@ -9,7 +9,7 @@ metadata:
   ms.date: 12/19/2019
   ms.service: dms
   ms.topic: landing-page
-  ms.custom: azure-migrate-seo
+  ms.custom: seo-azure-migrate
 
 # linkListType: architecture | concept | deploy | download | get-started | how-to-guide | learn | overview | quickstart | reference | tutorial | video | whats-new