Align DAST Site Token URL validation

What does this MR do and why?

this merge request fixes an issue for a customer who was unable to create a dast site token for a non-public url. it does this by bringing dast site profile and site token url validation into alignment through the creation of a common validation concern.

How to set up and validate locally

1. start up your local gdk
2. create a project
3. navigate to your dast profile library e.g. http://gitlab.localdev:3000/root/your-project/-/security/configuration/profile_library#site-profiles
4. create a dast site profile with the url in the linked confidential issue
5. click on the validate link in the dast site profile index

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.