add PaketBoostrapping target

Author: enricosada

src/Paket.Core/embedded/Paket.Restore.targets

@@ -39,7 +39,11 @@
     <DisableImplicitSystemValueTupleReference>true</DisableImplicitSystemValueTupleReference>
   </PropertyGroup>
 
-  <Target Name="PaketRestore" Condition="'$(PaketRestoreDisabled)' != 'True'" BeforeTargets="_GenerateDotnetCliToolReferenceSpecs;_GenerateProjectRestoreGraphPerFramework;_GenerateRestoreGraphWalkPerFramework;CollectPackageReferences" >
+  <Target Name="PaketBootstrapping" Condition="Exists('$(PaketToolsPath)paket.bootstrapper.proj')">
+    <MSBuild Projects="$(PaketToolsPath)paket.bootstrapper.proj" Targets="Restore" />
+  </Target>
+
+  <Target Name="PaketRestore" Condition="'$(PaketRestoreDisabled)' != 'True'" BeforeTargets="_GenerateDotnetCliToolReferenceSpecs;_GenerateProjectRestoreGraphPerFramework;_GenerateRestoreGraphWalkPerFramework;CollectPackageReferences" DependsOnTargets="PaketBootstrapping">
 
     <!-- Step 1 Check if lockfile is properly restored -->
     <PropertyGroup>