Improve organization of CI workflow scripts and pip requirements (#45037)

.github/workflows/bin/execute_installer.ps1

@@ -0,0 +1,7 @@
+$ proc = Start-Process  ${{ env.spack_installer }}\spack.exe "/install /quiet" -Passthru
+$handle = $proc.Handle # cache proc.Handle
+$proc.WaitForExit();
+
+if ($proc.ExitCode -ne 0) {
+    Write-Warning "$_ exited with status code $($proc.ExitCode)"
+}