Add User Migration trigger during `amplify add auth`?

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**Which Category is your question related to?**
auth

**Amplify CLI Version**
4.21.2

You can use `amplify -v` to check the amplify cli version on your system

**What AWS Services are you utilizing?**
Cognito, Lambda

**Provide additional details e.g. code snippets**

How do I configure a User Migration trigger during the setup of a user pool via Amplify? I'm able to create many other triggers (PostAuthentication, PreSignUp, etc.) but not UserMigration.