Specify connection config via an object and not string

Sorry if I'm blind, but how can I specify the connection with an object and not a string? E.g.

```js
mongoose.connect({
username: 'user123',
password: 'pass123',
host: 'mongodb0.example.com',
port: 1234,
})
```

Start by reviewing the mongoose.connect entry point and its existing connection configuration handling. Compare the requested object containing username, password, host, and port with the currently supported connection input, then establish whether object configuration should be supported and what completed behavior should be documented or tested.

Written by the indexing model from the issue text.