Greetings, @Vishal Singh , thanks for showing interest in this Preview feature.
Given that this is still a preview feature, my recommendation is to follow the documented steps to deploy the sample exemption policy.
However, if there's a business need to use Azure DevOps pipeline then check out Andrew's public blog on how to deploy policy initatives from an Azure devops pipeline.
Disclaimer: Yet to personally test the Azure policy/DevOps scenario described in blog but from my review this should meet your needs.
Dont hesitate to ping if you run into any issues or have any followup questions
Hope this helps.
Cheers.