Support users managed by an external directory in Jira during Sandbox Data Copy

Issue Summary

If in the Parent site there's an external directory managing the users besides the Jira internal, the users will not be imported to Sandbox and the copy process will fail. 

Steps to Reproduce

1. Integrate any External directory to manage the users, e.g. Crowd, AD in Jira
2. Add users to this external directory and they will be properly created in Jira and they're associated with this external directory.
3. Start the copy data process to Sandbox.

Expected Results

The users from both the internal and external directories would be imported into Cloud.

Actual Results

The copy process fails and this error is shown in SBAS:

"ValidationProgress(status=FAILED, rawProgress=100, subtask=null, message=, errors=[We have detected users from external directories. <a href="https://confluence.atlassian.com/jirakb/migrating-from-external-directory-to-jira-internal-user-directory-968659306.html" target="_blank">Convert your external directory to internal ones on server</a>, take a fresh backup, import again. <a href="https://confluence.atlassian.com/cloud/determine-your-user-migration-strategy-991930388.html" target="_blank">Learn more</a>.])"

Workaround

Migrate the users from the external directory to the internal directory in the Parent instance prior to copying data.