Update VTSH task

[e1turin]

• VTPC task require to run VTSH io-bench with new DIY page cache. So it should be designed to be ready to use dynamic lib
• add note about efficiency metric
• clearly state what really we want to determine with analysis (if it isn't yet)
• Shell measures time for 'task' execution. It should allow running N same commands in parallel as a single 'task'. This joins 1st part with 2nd. And in such way we can make benches to run with threads.
  • so, benches should be implemented as functions (built-in commands)
• remove ema- bench as hard to understand. Or remove/fix subtask of mixing io- and cpu- benches with threads.
• mb io- bench must be provided with fixed parameters in this lab, These parameters will be variated in next lab. Specify file size to work with; note how to work with it in parallel, how to store it, how to open (shared?).
  • add -iter flag to make bench more time-consuming.
  • read / read+write
• add reference to libc manual: https://sourceware.org/glibc/manual/
• add logging in Perfetto format for future visualization - provide library functions, as it is not trivial to work with json from C.