[EH] Run mgmt livetests in new pipeline

[swathipil]

Summary

Currently, mgmt live tests are not being run for this SDK. After a discussion with @ jsntcy and @ scbedd, it was decided that we want these tests to be run once every week in a new pipeline specifically for running mgmt tests.

Scope of Work

• Duplicate tests.yml​ file into a tests-mgmt.yml​ file.
• In the tests-mgmt.yml​ file:
• Add all environment variables necessary for mgmt tests to run.
• Remove all env vars that are not needed by mgmt tests and only by data plane tests.
• Specify azure-mgmt-eventhub ​as the target.
• Push the branch with this tests-mgmt.yml ​file change upstream.
• Create a new build/pipeline for running only the mgmt tests and schedule it to run once weekly.
• In the new pipeline, set the Branch/Tag ​param to the upstream branch with the tests-mgmt.yml file changes.

Success Criteria

• azure-mgmt-eventhub tests run once every week and pass.

[swathipil]

https://dev.azure.com/azure-sdk/internal/_dashboards/dashboard/65e61acc-b83a-4224-85a8-ffea0a147a59