tailscaled-env.txt does not apply on macos GUI installs

### What is the issue?

Feature is highly undocumented but according to code comments from this [this](https://github.com/tailscale/tailscale/commit/73d128238e123c92af985fee6e1d7c78c09e4d99) commit it should be visible under ~/Library/Containers/io.tailscale.ipn.macsys/Data/tailscaled-env.txt which is where the HOME within the sandbox should be. But that directory does not even exist and even if you make it, tailscaled-env.txt is not applied. Going by code logic it should be under the home of one of the ~/Library/Containers tailscale folder homes, which are **/Data/, but putting tailscaled-env.txt under none of them work.

```
./io.tailscale.ipn.macsys.share-extension/Data/tailscaled-env.txt
./io.tailscale.ipn.macsys.login-item-helper/Data/tailscaled-env.txt
./io.tailscale.ipn.macsys/Data/tailscaled-env.txt
```

### Steps to reproduce

Add tailscaled-env.txt files to destinations as given by https://github.com/tailscale/tailscale/blob/main/envknob/envknob.go comments for the standalone and app store versions

Checkable using TS_DEBUG_MTU values and ifconfig

### Are there any recent changes that introduced the issue?

_No response_

### OS

macOS

### OS version

_No response_

### Tailscale version

1.68.1

### Other software

_No response_

### Bug report

_No response_