Updating TS resets its Windows service configuration

### What is the issue?

On Windows, updating Tailscale resets/overrides the configuration of the Tailscale service

### Steps to reproduce

1. Install Tailscale
2. Modify its configuration (e.g. change its Windows Service startup mode via `SC CONFIG "tailscale" start=demand`)
3. Update Tailscale by running the installer for the next version (e.g. `winget update -id Tailscale.Tailscale`)
4. Open Services.msc and view the Tailscale service's Properties

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

No.

### OS

Windows

### OS version

Windows 11

### Tailscale version

1.98.90

### Other software

N/A

### Bug report

N/A

Start by tracing the Windows installer and Tailscale service configuration path used during an update, then reproduce the issue with `SC CONFIG "tailscale" start=demand` and `winget update -id Tailscale.Tailscale`. Done means an update preserves the service startup mode and other existing Windows service configuration.

Written by the indexing model from the issue text.