Improve Multithreaded Performance of azure_messaging_eventhubs ProducerClient

[devinjdangelo]

Feature Summary

Remove Mutex<> locks in ProducerClient which block threads when ProducerClient is shared accross threads.

Feature Description

ProducerClient makes liberal use of Mutex for thread safety, so there is no performance improvement if a single ProducerClient is shared across threads. We could instead implement connection pooling or thread local connections to improve multithreaded performance.

Use Case

Using ProducerClient as a singleton shared with many threads.

Alternatives

Don't use ProcuerClient as a singelton, guide customers to initialize a new one on each thread.

Additional Context

No response