Add support for port forwarding

[Shocktrooper]

The devcontainer specification supports port forwarding as part of the definition. This appears to not be supported in the current version of envbuilder

https://containers.dev/implementors/json_reference/#port-attributes

[jbadeau]

Been open for a while? What’s the status?

[lornest]

Came looking for an update on this too. Is there an alternate suggestion to port forwarding in devcontainers.jsonwhen using this with Coder?