Feature: Dynamic port forwarding allow+deny list

[gtaylor]

I posted a feature request for an allow+deny list for port forwarding on the jetbrains-backend-coder repo, but this also applies to the VS Code case. Cross-posting the issue here so we can separately track these for both IDEs:

Here is the JB version of the issue: https://github.com/coder/jetbrains-backend-coder/issues/38

[aaronlehmann]

Note that this can be done without explicit support in the Coder extension: the remote.portAttributes and remote.otherPortAttributes VS Code settings can be set through ~/.vscode-server/data/Machine/settings.json on the workspace.

If this is being driven by devcontainer.json, it's sufficient to copy portAttributes from devcontainer.json to remote.portAttributes in settings.json (and so on for otherPortAttributes), since the devcontainer.json schema for these matches VS Code's settings schema.