DAST configuration - update unvalidated site profile alert banner

What does this MR do and why?

This updates the alert that's shown when conflicting DAST profiles are selected:

• The message has been made clearer.
• The primary button now points to the site profile management.

A bit of refactoring has been done too:

• The alert has been moved to its own Vue component so that the same code can be reused in on-demand scans and in the DAST configuration form.
• Translations have been moved to the component's options.
• The dastSiteValidationDocsPath is now constructed in the frontend exclusively.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Visit the DAST configuration form at /:namespace/:project/-/security/configuration/dast.
   1. Select an active scanner profile and a non-validated site profile.
2. Visit the on-demand DAST scan form at /:namespace/:project/-/on_demand_scans/new.
   1. Select an active scanner profile and a non-validated site profile.

Related to #340345 (closed)