Correctly handle sending signal to child process

[belimawr]

What does this PR do?

Calling proc.Kill causes the process to exit immediately, which
prevents components from executing some clean up functions.

To gracefully terminate the components, on Linux and MacOS SIGTERM
is sent.

On Windows signals are sent to process groups, child process are created
in the same group as the parent, so sending a signal to a child process
causes the Elastic-Agent to receive the signal as well. Therefore child
process need to be created in their own process group.

To do so, the child process needs to be created setting the creation flag
CREATE_NEW_PROCESS_GROUP, which has the side effect of disbling
the CTRL+C signal.

Then to correctly terminate the child process windows.GenerateConsoleCtrlEvent
is called to send CTRL+BREAK signal that is translated by go Go runtime into a
syscall.SIGINT, which is already correctly handled by Beats.

Why is it important?

It correctly signals components to exit, allowing them to run their cleanup.

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

## Disruptive User Impact

How to test this PR locally

mage build:TestBinaries cd pkg/core/process go test . 

Related issues

• Partially fixes Beats shutdown issue #6875
• Relates to Elastic-Agent does not allow child process to clean up during shutdown #7756

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[mergify]

This pull request does not have a backport label. Could you fix it @belimawr? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-./d./d is the label that automatically backports to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[belimawr]

buildkite test this

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
50.0% Coverage on New Code
3.1% Duplication on New Code

See analysis details on SonarQube

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 6c14b82

History

• 💔 Build #19714 failed e59769c

cc @belimawr

[blakerouse]

Thanks for working on this. Windows hard-stopping everything is not good, this was really needed! Nice work.

[belimawr]

Thanks for working on this. Windows hard-stopping everything is not good, this was really needed! Nice work.

Thank you @blakerouse!

Btw, be aware that this PR does not fully fixes the problem, sub process will still be forcefully killed until #7756 is resolved.