Add DAST Site Validation GraphQL query endpoint

• #245213 (closed)

What does this MR do?

This MR adds the GraphQL query endpoint for a DastSiteValidation.

query project($fullPath: ID!, $targetUrl: String!) {
  project(fullPath: $fullPath) {
    dastSiteValidation(targetUrl: $targetUrl) {
      id
      status
    }
  }
}

The MR relates to #245213 (closed)

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Does this MR meet the acceptance criteria?

Conformity

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