* Added blocking Open for message sender
* Blocking message sender open; added AZURE_NODISCARD to help ensure APIs that are likely to fail have their returns checked
* Update eventhubs stress test to use DefaultAzureCredential instead of ClientSecretCredential; Fixed stress test to correctly request client parameters; Removed hard coded resource name from producer client test
* Pull request feedback with link events; renamed AZURE_NODISCARD to _azure_NODISCARD
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Co-authored-by: Rick Winter <rick.winter@microsoft.com>
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