feat(tools): Add script to flamegraph a command

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

bin/__dispatch.sh

@@ -40,6 +40,9 @@ case "${TARGET_TOOL}" in
   ninja)
     attr="third_party.ninja"
     ;;
+  perf-flamegraph)
+    attr="tools.perf-flamegraph"
+    ;;
   rebuild-system)
     attr="ops.nixos.rebuild-system"
     ;;