Agentic code review not available with Duo Enterprise trial license in 18.7.1

In 18.7.1 adding gitlabduo as a reviewer is still using the "classic" code review instead of agentic, blocking further testing of agentic code review, which is the top use case. The customer is looking for a solution to continue testing.

Notes:

1. Due to history of the evaluation the customer is using a Duo Enterprise trial license
2. There was a decision to allow users to access "classic" code review when using a Duo Enterprise license starting in 18.7 as part of the transition to GA

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This issue was created based on https://gitlab.com/gitlab-com/account-management/western-north-america/cisco-group/splunk-group/splunk-duo-sm-self-hosted-models-pov/-/issues/78