Migrate pallet-election-provider-support-benchmarking benchmark to v2 (#6315)

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>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>