Add a custom serializer

[johnnyasantoss]

Is your feature request related to a problem? Please describe.
When working with BigInt or any other JS Type that isn't natively supported on JSON (or JSON.stringify) we have no good solution other than manually transform string serialized values back to their original format/type.

Maybe related #2771

Describe the solution you'd like
Have a global hook bullmq.serialize = async (data) => ... that is overridable by the user.

Describe alternatives you've considered
Manually converting back properties one by one - tedious and error prone

[godinja]

Some additional context here #2591

[johnnyasantoss]

Thank you @godinja. This is probably a dupe of #14 but highlights our need of supporting bigints which is not supported by json (not directly at least)