Add 'remoteUserHome' variable to `devcontainer-feature.json`

Scenario - In `devcontainer-feature.json` I’d like to do update the `containerEnv.PATH` as follows 👇

```jsonc

"containerEnv": {
"PATH": "${remoteUserHome}/.local/bin:${PATH}"
}
```

where the `remoteUserHome` can be `/root` or `/home/userName` depending upon the remote user. Currently, I am not able to add the following to the `PATH` because the remote user is dynamic and hardcoding wouldn't work.

As `remoteUserHome` is available during running feature scripts, I wonder if they could be available when the `containerEnv` merge logic is implemented?

I also tried to add `~/.local/bin` to the PATH, however, that doesn't work if a shell is not invoked. Hence, doesn't help in my scenario.