Add `rabbitmq-key` to the list of secrets requiring migration in 4.2 [ONPREM-1276]

[christian-stephen]

Description

A brief description of the changes.

The RabbitMQ secret requires an annotation if self-managed during a 4.1 -> 4.2 migration. However, it was missed on the list of secrets requiring intervention. This PR addresses that.

Reasons

A link to a GitHub and/or JIRA issue (if applicable). Otherwise, a brief sentence about why you made these changes.

https://circleci.atlassian.net/browse/ONPREM-1276

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