Fix environment creation with prevent_self_review

[igorcosta]

Related to #628

Implements validation and error handling for environment creation with prevent_self_review enabled in lib/plugins/environments.js.

• Updates the environment creation and update logic to ensure that at least one reviewer is present when prevent_self_review is set to true. This prevents the creation of environments without reviewers, addressing the issue where environments were partially created on the first attempt and required a restart to complete.
• Adds error logging to clearly indicate when the creation process is halted due to the absence of reviewers, improving the visibility of the issue and aiding in troubleshooting.
• Ensures that environments with the correct configuration of reviewers and prevent_self_review are created successfully in a single pass, eliminating the need for partial provisioning or errors that lead to pod restarts.