Need for shutdown_async?

[cijothomas]

PeriodicReader and BatchProcessors have been redesigned to create own Thread and make blocking calls from within it.
A shutdown is triggered by the Drop, which can block user thread. Options

1. Offer a shutdown_async() variant, which users can invoke themselves and await. Once shutdown is already initiated, drop will not re-attempt, so there won't be a concern about Blocking user threads.
2. Have users rely on methods offered by async runtimes like tokio::spawn_blocking to invoke shutdown.

Opening a tracking issue to collect feedback on this, before exposing a new API.

[lalitb]

The providers currently do not offer any async API. I would vote to keep the existing design and allow users to rely on async blocking mechanisms to invoke shutdown (i.e. option 2 above).