Settings CI/CD: harmonise warning alerts

Following "Add warning when Token Access disabled" !98123 (merged)

Problem

Settings CI/CD uses mixed design for warning messages

Proposal

Harmonise style by using Gitlab Alert (GlAlert) everywhere, like in Token Access !98123 (merged)

Todo:

• Use Gitlab Alert in "Protected environments"
• Use Gitlab Alert in "Variables"
• Use Gitlab Alert in "Pipeline triggers"