migrate pallet-nomination-pool-benchmarking to benchmarking syntax v2 (#6302)

Migrates pallet-nomination-pool-benchmarking to benchmarking syntax v2.

Part of:
* #6202

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Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Guillaume Thiolliere <guillaume.thiolliere@parity.io>
Co-authored-by: Giuseppe Re <giuseppe.re@parity.io>

prdoc/pr_6302.prdoc

+title: migrate pallet-nomination-pool-benchmarking to benchmarking syntax v2
+doc:
+- audience: Runtime Dev
+  description: |-
+    migrate pallet-nomination-pool-benchmarking to benchmarking syntax v2
+crates:
+- name: pallet-nomination-pools-benchmarking
+  bump: patch