Add tools.perf-flamegraph, which collects the base case execution of
perf piped through stackcollapse-perf and flamegraph to flamegraph the
execution of an external command via perf.
Change-Id: I671fe254dc374b6cd7deca2d3bdea266164de025
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1176
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI
