Port forward: multiple localPort for a same resource

What I'm trying to do: forward a service port to two hosts ports so I have `localhost:XXX` and `localhost:YYY` binded to the same resource and port.

### Expected behavior

Being able to set the same `portForward` rule two times with just a different `localPort` (but same `namespace`, `resourceType`, `resourceName` and `port`).

### Actual behavior

Skaffold forwards only the first entry.

### Information

- Skaffold version: `1.26.1`
- Operating system: Fedora Silverblue 34 (`34.20210620.0`)
- Installed via: downloaded the binary release from Github
- Contents of skaffold.yaml:

```yaml
…
portForward:
- namespace: ambassador
resourceType: service
resourceName: ambassador
port: 443
localPort: 10000
- namespace: ambassador
resourceType: service
resourceName: ambassador
port: 443
localPort: 4200
…
```

### Steps to reproduce the behavior

1. setup a service which listen on a port (here, installed Ambassador Edge Stack)
2. setup `portForward` twice for this service and port but with two different local ports
3. run `skaffold dev`
4. try `curl localhost:XXX` and `curl localhost:YYY` for both ports, see only one is opened

### Logs

#### Expected

Seeing two ports forwarded.

```
Port forwarding service/ambassador in namespace ambassador, remote port 443 -> 127.0.0.1:10000
Port forwarding service/ambassador in namespace ambassador, remote port 443 -> 127.0.0.1:4200
```

#### Actual

Missing one forwarding.

```
Port forwarding service/ambassador in namespace ambassador, remote port 443 -> 127.0.0.1:10000
```

If I put the `4200` forward before the `10000` forward, the `4200` is used (so I guess Skaffold uses the first `portForward` rule when you have multiple rules with only a changing `localPort`).