* Re-open the log file on OS Signal trigger

This PR implements an handler for the CONT signal.
The handler will close and re-open the log file.
If the log destination is not a file, this is a no-op.

Useful for logrotate postrotate hook.

* signal replaced with the fsnotify

* code review changes:
- refactored to launch watcher with process context
- make file shared writer as singleton
- add test for logrotate case

* add locking for write, reopen

* - configuration for log section update
- test simplification

* code review changes:
- add closing for file shared writer
- make runWatcherFunc not exported

* linter fixes

* change default file mode for log file
simplify setting global watcher

* terminate watcher after override global one
added test for validating global override

* make log file name static for shared writer

* replace logic to use finalizer instead

* fix possible locking write while reopen is triggered

* wrap internal error, fix incorrect unlock

* drop configuration flag, make watcher always enabled

* tune context passing

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Co-authored-by: Vadym Popov <vadym.popov@goteleport.com>

…te-v16