🐛Service install does not respect generic args or environment variables

**Describe the bug**
When running `cloudflared service install` it is not possible to pass additional arguments or environment variables for the service installation. This makes it notably more difficult to create tunnels using tools like Ansible on an IPv6-only device where those arguments are necessary to create the tunnel (since the command will stall while waiting for the tunnel to become available). This means the entire service file has to be created (and kept in sync with this repo) to avoid manual intervention.

**To Reproduce**
Steps to reproduce the behavior:
1. Configure a remote tunnel via the dashboard
2. Run 'cloudflare service install --edge-ip-version=6 ...' (also get same output is use a space instead of `=`)
3. See error of "Incorrect Usage: flag provided but not defined: -edge-ip-version"
4. Run `TUNNEL_EDGE_IP_VERSION=6 cloudflare service install ...`
5. See command create the systemd service and then stall

If it's an issue with Cloudflare Tunnel:
4. Tunnel ID : (did not finish registering/creating/connecting; does not appear in dashboard)
5. cloudflared config: N/A (remote tunnel)

**Expected behavior**
The systemd unit should either pass in generic arguments to the `{{ range .ExtraArgs }}` or add the `TUNNEL_` environment variables to the systemd unit file (or automatically create an override with those included)

**Environment and versions**
- OS: Debian 13 (Trixie) via the Debian "any" package repo
- Architecture: x64
- Version: 2025.8.0

**Logs and errors**
CLI output when running service install via environment variable (stalls):

```shell
# cloudflared service install ...
2025-08-15T01:52:15Z INF Using Systemd
^C
```

CLI output when running service install via arguments:

```shell
# cloudflared service install --edge-ip-version=6 ...
Incorrect Usage: flag provided but not defined: -edge-ip-version
```

**Additional context**
Defaulting `EdgeIpVersion` to `auto` would solve my immediate issue but this would also be desirable for setting a bind address, force PQ only, or to only use the US region