[service] windows service, receive multiple change requests

[leehinman]

What does this PR do?

In the windows service Execute function, use for loop to receive all the change requests not just the first one.

Why is it important?

Without this only the first change request is received. So if the service is sent Interrogate, followed by Shutdown, it would only see the Interrogate request and never receive the Shutdown request.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.md

Author's Checklist

• [ ]

Related issues

• Windows tests can fail during uninstall with "The service cannot accept control messages at this time" causing cascading test failures elastic-agent#3557
• occasional uninstall hang on Windows 8.8.1 elastic-agent#3372
• Elastic Agent is not notifying the Windows service manager that it is about to shut down reliably elastic-agent#3307
• Unable to Start/Restart a Windows Service After Installing Elastic Agent v8.7.1 or Newer elastic-agent#3061
• Windows tests can fail during uninstall with "The service cannot accept control messages at this time" causing cascading test failures elastic-agent#3557

[cmacknz]

🚢

[cmacknz]

Both Beats and Agent will need this fix.

[elasticmachine]

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