Microsoft-graph-docs: Broken link to notification endpoint validation

[fredericklin]

Issue:
The documentation on notification endpoint validation used to be in this article. Now I think that information has been moved to a link that does not exist. See the link "notifications for changes in user data" in the "Create Subscription" doc.

Article:
https://developer.microsoft.com/en-us/graph/docs/api-reference/v1.0/api/subscription_post_subscriptions
https://developer.microsoft.com/concepts/webhooks#notification-endpoint-validation

[jthake-msft]

Thanks for flagging this @angelgolfer-ms is this something you can fix?

[fredericklin]

Getting ready for GA? :) Noticed duplicate articles in /v1.0 and /beta

[jasonjoh]

That's my bad, I'll fix it.