Fix(Core): Agent request handle as system user

[stonebuzz]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
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Description

• It fixes "No active session" when agents with scheduled tasks try to communicate with the server #792

Agent request handle as system user

Screenshots (if appropriate):

[trasher]

While this fix the issue the user has reported, I'm not sure it's the correct way to go; see our internal channel.

[stonebuzz]

While this fix the issue the user has reported, I'm not sure it's the correct way to go; see our internal channel.

done !

[trasher]

While this fix the issue the user has reported, I'm not sure it's the correct way to go; see our internal channel.

done !

I'm not sure we should keep the call as system if we force the interface.

[trasher]

LGTM