Improper shutdown on Windows causing issues with integrations

[AndersonQ]

tl;dr:

• on Windows a CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT or CTRL_SHUTDOWN_EVENT is sent as a syscall.SIGTERM to [signal.Notify]
• the code dealing with the SCM might not be triggered when a syscall.SIGTERM is received
• the shutdown code relies on defer which does not run when os-Exit is called.

A detailed explanation is found on elastic/elastic-agent#1525. This issue is seen in the Elastic Agent, and part of the problem resides on the elastic-agent-libs