Support continuous process I/O profiling

[mrueg]

It would be interesting to enhance parca with data for I/O operations per second and latency in addition to the CPU-based profiling, so a user can figure out if a process is CPU- or IO-bound. For disks, I guess right now it's possible to take a look at the vfs_read syscalls, it could be helpful to visualize I/O access in a separate view.

https://github.com/iovisor/bpftrace/blob/master/docs/tutorial_one_liners.md#lesson-7-timing-reads https://github.com/iovisor/bcc/blob/master/tools/biolatency_example.txt https://github.com/iovisor/bcc/blob/master/tools/biotop_example.txt

[brancz]

Related: https://github.com/parca-dev/parca-agent/issues/239