Custom port forwarding

Sometimes, people need to expose custom ports themselves.

Instead of increasing the ports list or dir, we could have a section for custom ports, like:

## Option 1
```
chains:
- id: osmosis-1
name: osmosis
ports:
rpc: 2657
custom:
- name: eth-http-jsonrpc
target: 8467
port: 8467
```

## Option 2:
```
chains:
- id: osmosis-1
name: osmosis
ports:
rpc: 2657
customPorts:
- name: eth-http-jsonrpc
target: 8467
port: 8467
```

Custom ports could be more open ended, and anything from a service can be opened up with custom ports.