Resolve "Test, update, and fix or remove `preflight-check`"

General MR

Summary

Add messaging to indicate when registry credentials were not properly provided, add a delay for existing namespace deletion to ensure the command will work properly when run multiple times in quick succession, and update the unit test to include non-empty config values for the registry credentials.

Linked Issue

#55 (closed)

Upgrade Notices

N/A

Closes #55 (closed)