[Feature Request] Add thread lifecycle hook to `Worker::ThreadPool`

[chris-olszewski]

Is your feature request related to a problem? Please describe.

Need to acquire/release resources at the thread level.

Describe the solution you'd like

A new Temporalio::Worker::ThreadPool::ThreadContext with a single call method takes a block. A thread context can be provided when initializing a new thread pool. For each thread started, have the context invoked with the worker job loop.

Additional context