This was already possible on Linux if you ran tailscaled with --debug
(which runs net/http/pprof), but it requires the user have the Go
toolchain around.
Also, it wasn't possible on macOS, as there's no way to run the IPNExtension
with a debug server (it doesn't run tailscaled).
And on Windows it's super tedious: beyond what users want to do or
what we want to explain.
Instead, put it in "tailscale debug" so it works and works the same on
all platforms. Then we can ask users to run it when we're debugging something
and they can email us the output files.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
