Fix alignment of global alerts

📖 What does this MR do?

Related to #326732 (closed)

Fixes alignment of "Open registration is enabled on your instance." and "Auto DevOps enabled" global alerts. To ensure that styles will be consistent across all global alerts this MR also creates a new _global_alert.html.haml partial. Once this is merged issues will be opened to refactor all other global alerts to use the _global_alert.html.haml partial.

💻 Local testing

1. Delete the hide_auto_devops_implicitly_enabled_banner_<project_id> cookie
2. Delete the UserCallout record for the "Open registration is enabled on your instance." alert
   • bin/rails console
   • UserCallout.where({ feature_name: 25 }).destroy_all
3. Navigate to a project

📷 Screenshots

Before	After

🚦 Does this MR meet the acceptance criteria?

Conformity

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