[CWS] Send SIGHUP when reloading system-probe systemd service

[lebauce]

What does this PR do?

CWS has been supporting reloading policies for some time by sending a HUP signal.
Bind this mechanism to systemd service.

Motivation

Additional Notes

Possible Drawbacks / Trade-offs

Describe how to test/QA your changes

Reviewer's Checklist

• If known, an appropriate milestone has been selected; otherwise the Triage milestone is set.
• Use the major_change label if your change either has a major impact on the code base, is impacting multiple teams or is changing important well-established internals of the Agent. This label will be use during QA to make sure each team pay extra attention to the changed behavior. For any customer facing change use a releasenote.
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• Changed code has automated tests for its functionality.
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• If applicable, the k8s/<min-version> label, indicating the lowest Kubernetes version compatible with this feature.
• If applicable, the config template has been updated.