How to automate creating credentials in a secure way
You can leverage PowerShell and the Thycotic REST API to fetch your credentials from Secret Server programmatically. Use "Windows Authentication" to avoid having to store credentials in the PowerShell scripts, or enter them during runtime. 

If your deployments run under a build agent service account context, then you need to ensure that service account has access in Secret Server to the credentials you want to access.

Leveraging the API as a step in your release prior to deploying the SQL credential, you can fetch the credential and pass it to the PowerShell script that deploys the credential.