feat: data plane data source

[matt-FFFFFF]

Adds data plane data source for existing supported services

[simongottschlag]

Howdy @matt-FFFFFF!

I just came here looking for a way not to have to write my own provider to be able to read App Configuration keys through its data plane. Using azapi/azurerm, I must at least have the permission to read the endpoint (or at least from what I have figured out so far).

This PR would most likely solve my use case being able to provide landing zones read access to App Configuration and use it as an authoritative source for information (like mapping landing zones ids to subscription ids and group object ids).

So just an heads up that this would be awesome and maybe a small question if you have any plans on merging it or if you would like any help from me 😊

As always, thanks! 🙏