TEST-0010 Add NET 9 target, update packages and switch to project fol…

…der (#368)

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src/backend/Directory.Build.props

@@ -17,6 +17,10 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <AssemblyAttribute Include="WebApi.Attributes.DefineConstantsAttribute">
+      <_Parameter1>"$(DefineConstants)"</_Parameter1>
+    </AssemblyAttribute>
+
     <NuGetAuditSuppress
       Include="https://github.com/advisories/GHSA-5f2m-466j-3848;https://github.com/advisories/GHSA-x5qj-9vmx-7g6g;https://github.com/advisories/GHSA-xhfc-gr8f-ffwc" />