Please provide us with the following information:

This issue is a: (mark with an x)

• [ X] bug report -> please search issues before submitting
• documentation issue or request
• regression (a behavior that used to work and stopped in a new release)

Issue description

I noticed that when using the az containerapp up command in my azure devops pipeline to update a container app with a new image the custom domains are all cleared.

Steps to reproduct

1. Create a container app custom domain
2. Update container app via command line (az containerapp up)
3. Check custom domains

Expected behavior [What you expected to happen.]
Custom domains remain

Actual behavior [What actually happened.]
custom domains are cleared

Additional context

Ex. Did this issue occur in the CLI or the Portal?
Occurs via cli but visible in portal