add new RUBY_BENCH_CMD_PREFIX option #1898

Job	Run time
benchmark-ractor (head)	6m 40s
test (truffleruby)	1m 48s
test (ruby)	52s
benchmark-default (truffleruby, --excludes=knucleotide,lobsters,ruby-lsp,shipit)	12m 42s
benchmark-default (head)	12m 39s
benchmark-run-once	1m 37s
benchmark-ractor-only (head)	39s
test (head)	41s
benchmark-graph	51s
benchmark-default (ruby)	11m 31s
all-tests	3s
	50m 3s

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