Retrieve the list of signature enrollments.

Retrieve the list of enrollments that use signature as the authentication method.

The signature authentication method refers to the use of a digital signature as a second factor to authenticate an external entity.

Entitlements:
- manageEnrollMFAMethodAnyUser (Manage second-factor authentication enrollment for all users)
- manageEnrollMFAMethod (Manage own second-factor authentication enrollment)
- readEnrollMFAMethodAnyUser (Read second-factor authentication enrollment for all users)
- readEnrollMFAMethod (Read own second-factor authentication enrollment)