Tool to tune system parameters like PoH service priority

[pgarg66]

Problem

The PoH service thread scheduling policy and priority cannot be tuned unless we use a shell script. Using the shell script is not a viable option for external nodes.

Summary of Changes

Added a new daemon sys_tuner that runs at a higher privilege. It listens on a local domain socket. When validator boots up, the poh_service connects to the socket. It triggers the sys_tuner to look up poh_service's thread ID, and adjust its priority and scheduling policy.

Fixes #6482

[codecov]

Codecov Report

Merging #7155 into master will decrease coverage by 0.1%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #7155     +/-   ##
========================================
- Coverage    72.8%   72.6%   -0.2%     
========================================
  Files         234     235      +1     
  Lines       49719   49787     +68     
========================================
- Hits        36196   36193      -3     
- Misses      13523   13594     +71

[mvines]

Move

solana/scripts/tune-system.sh

Lines 34 to 38 in 5a30ef1

	# Reference: https://medium.com/@CameronSparr/increase-os-udp-buffers-to-improve-performance-51d167bb1360
	sysctl_write net.core.rmem_max 134217728
	sysctl_write net.core.rmem_default 134217728
	sysctl_write net.core.wmem_max 134217728
	sysctl_write net.core.wmem_default 134217728

into sys-tuner as a follow-up?

It would be good to add some documentation about solana-sys-tuner into book/src/book/src/running-validator/validator-start.md

Pull request has been modified.