Create/Update docs to capture container --> UDT connection and udt--> udt

[nithyatsu]

What content needs to be created or modified?

We can now have a container connect to UDT to get some variables auto-injected as environment variables.
We should have some content capturing sample manifest, bicep and how-to that enables understanding this feature.

Describe the solution you'd like

Where should the new material be placed?

The associated pull request from the Radius code repo, if applicable

Additional context

AB#15809