Specify port number with go-discover syntax for primary_gateways

When creating a WAN federation via mesh gateways with ACL replication, the secondary datacenter config must include the `primary_gateways` option, pointing to the first datacenter's mesh gateways.

[The docs](https://www.consul.io/docs/connect/gateways/mesh-gateway/wan-federation-via-mesh-gateways#consul-server-options) suggest that [go-discover syntax](https://www.consul.io/docs/install/cloud-auto-join) can be used. However, as opposed to the `retry_join` and other options, which only require an IP address, `primary_gateways` also requires a port to be specified (e.g. `primary_gateways = ["1.2.3.4:8443"]`. Therefore, how can the port number be appended after the `go-discover` syntax? I tried something along the lines of
```
primary_gateways = ["provider=aws tag_key=\"key\" tag_value=\"value\":8443"]
```

but it does not work.

The Consul version used is `1.12.0-1`.