Fix http_proxy service dir in k3s_agent role

[balazshasprai]

Proposed Changes

I've noticed I messed up in the last commit regarding the http_proxy setup.
On nodes/workers/agents it should've put the http_proxy config in the k3s-node.service.d dir, instead it puts it in k3s.service.d.
This fixes that slip-up.

Checklist

• Tested locally
• Ran site.yml playbook
• Ran reset.yml playbook
• Did not add any unnecessary changes
• Ran pre-commit install at least once before committing
• 🚀

[tagn]

This will fix #397, I closed the PR that I submitted yesterday for this issue. Thanks for fixing it @balazshasprai