Documentation page for nested deployment scoping rules

[jeskew]

In #13612, a user asks if there is any documentation page describing what scopes can deploy to other scopes. The closest I could find was that in each page describing a particular deployment scope, there is a section on deploying to a different scope from that scope (e.g., deploying from RG -> other RG, subscription, or tenant scope, deploying from subscription to other subscription, RG, or tenant scope, deploying from MG -> other MG, subscription, RG or tenant scope, and deploying from tenant -> MG, subscription, or RG scope. As far as I can tell, the only forbidden scope transitions are from RG -> MG or from subscription -> MG, but we don't state that explicitly anywhere.

Should we have a dedicated page on which scope transition are allowed and which are disallowed? Or at least call out in the RG and subscription scope pages that MG-scoped deployments are forbidden?

[mumian]

@jeskew - can you review https://github.com/MicrosoftDocs/azure-docs-pr/pull/270242?