Allow user to validate site profile from `New on-demand DAST scan` page

From #290081 (comment 520638674)

Problem to Solve

TLDR: Allow users to validate a site profile from the "New on-demand DAST scan" page
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Site profile validation must be completed after a profile has been created (because reasons). The only place a site profile can be validated, currently, is from the site profile library.

When configuring a DAST scan, if a user selects a site profile that isn't validated, they're informed that the chosen profile isn't validated but are not given any information or actions for how to validate it. The only way users are notified that their profile may need to be validated is if they select an "active" Scanner Profile and an "unvalidated" Site Profile.

The problem is more pervasive when creating a site profile from the On-demand scan configuration page. After saving a new site profile, users are redirected back to the on-demand configuration page where their new profile is selected and marked as Not validated. For some users, this could be the first time they see anything about site validation and are not given the resources needed to understand what it means.

Proposal [WIP]

On the On-demand scan configuration page, we should:

• Inform users why they might need to validate a site profile if it isn't already validated (this will help them determine if it's something they need to be concerned with)
• Present users with a way to validate their site profile or learn more about the process

Supporting designs to come...