Proposal: Ability to configure msgpack encoding, e.g. to ignore undefined properties

Hi 👋

Would it be helpful to anyone else if it were possible to configure the msgpack encoder.

For example msgpack has the option to `ignoreUndefinedProperties`, which is desirable in certain circumstances, eg. to reduce bandwidth or storage requirements.

Msgpack options could (for example) be provided with the client configuration. Something like:

```js
const client = new FluentClient('tag', {
msgpackOptions: {
maxDepth: 42,
ingnoreUndefined: true,
// other msgpack options at https://github.com/msgpack/msgpack-javascript/blob/main/src/Encoder.ts#L15
}
}
```

Would be happy to throw something together if it's interesting.

Thanks in advance