feat(cli): Use SIGUSR2 to run sysctl commands

[msbrogli]

Motivation

Sometimes the CPU is so high that sysctl become irresponsive. So this PR adds another method to send command to sysctl.

Acceptance Criteria

1. Handle SIGUSR2 on cli run_node.
2. Create a named pipe to receive a list of sysctl commands, one per line.
3. Execute the sysctl commands and log their results.
4. The named pipe will be created at the data directory if it exists. Otherwise, a temporary folder will be created.
5. Add decorator @signal_handler_safe to mark setters as safe to be executed during a signal handling.
6. Add require_signal_handler_safe: bool = False to the SysctlRunner.run() method.
7. Rename _get_getter() and _set_setter() to get_getter() and set_setter() on Sysctl.
8. Rename set() to unsafe_set() on Sysctl. It also updates the docstring to explain that it is unsafe to call this method directly.
9. Mark max_enabled_sync, enabled_sync_versions and kill_connection as signal handler safe on ConnectionsManagerSysctl.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (f4d6a28) 85.34% compared to head (565377f) 85.26%.

Files	Patch %	Lines
hathor/sysctl/runner.py	75.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #949      +/-   ##
==========================================
- Coverage   85.34%   85.26%   -0.08%     
==========================================
  Files         291      291              
  Lines       22540    22553      +13     
  Branches     3393     3399       +6     
==========================================
- Hits        19236    19230       -6     
- Misses       2630     2643      +13     
- Partials      674      680       +6     

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