migrate pallet-session-benchmarking to bench V2 syntax #15090

Job	Run time
check-dependency-rules	7s
check-fail-ci	16s
check-markdown	15s
check-readme	3m 7s
check-workspace	18s
preflight / preflight	42s
preflight / ci-versions	1m 11s
check-rust-feature-propagation	2m 12s
fmt	1m 21s
test-rust-features	2m 13s
check-toml-format	1m 7s
check-umbrella	2m 34s
All quick checks passed	1s
	15m 24s

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