Move Dast::Profile association out of transaction

What does this MR do and why?

this merge request moves the creation of dast_profile assocations when creating an on-demand dast scan. this was necessary because creating x-database records inside the same transaction is not possible.

Related Issues

dast_site_profiles created during pipeline creation causes CrossDatabaseModificationAcrossUnsupportedTablesError

Dependencies

Fix dast_configuration keyword cross-join issue

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.