Connection management

Would be great if i can save named connections for a future quick connect

With that we could add a new predefined connection
```
mssql-cli add-connection -n "remote-server" -S 10.1.2.3 -U sa -W pass123
```

List the stored connections, showing only the name, server and user
```
mssql-cli list-connection
```

With that, on normal CLI we just pass the connection name for quick accesss

```
mssql-cli "remote-server"
```