Add support to create the subscription users while promoting

[waelkdouh]

Currently apiops expects the user to exist in the target apim instance before while promoting. This can cause the publisher to fail if the user doesn't exist in the target apim instance.

[github-actions]

  Thank you for opening this issue! Please be patient while we will look into it and get back to you as this is an open source project. In the meantime make sure you take a look at the [closed issues](https://github.com/Azure/apiops/issues?q=is%3Aissue+is%3Aclosed) in case your question has already been answered. Don't forget to provide any additional information if needed (e.g. scrubbed logs, detailed feature requests,etc.).
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