Rust-SDK: Add task_queue to ChildWorkflowOptions

[c-thiel]

What was changed

Add task_queue to rust-sdk ChildWorkflowOptions.

Why?

There was no option to specify the task queue for Child Workflows before.

Checklist

1. Closes
   [Feature Request] Rust SDK add option to specify task_queue for child workflows #642

2. How was this tested:

No dedicated test. Do we need one?

4. Any docs updates needed?

No

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}