Set DAST_API_HOST_OVERRIDE for on-demand API scans

What does this MR do?

ensures that DAST_API_HOST_OVERRIDE is set for on-demand API scans.

Why?

this is a simplification that ensures the host being scanned matches the one that has been validated. this is necessary because openapi v3 api specifications may contain multiple unrelated hosts, which could result in the wrong host being scanned.

Related Issue(s)

• #294060 (closed)

Does this MR meet the acceptance criteria?

Conformity

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  • I have included a changelog entry.
  • I have not included a changelog entry because the functionality that sets the model value is featureflagdisabled (:security_dast_site_profiles_api_option).
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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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Security

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