feat: auto-cleanup old/expired certificates and sync to strongSwan

[allen12921]

• Auto-remove old certificates when uploading new ones with same public key
• Cleanup expired certificates on strongSwan startup and sync via vici

This ensures strongMan database and strongSwan stay in sync when certificates are renewed or expired.

Changes:

• services.py: Remove duplicate certs with same public key on upload
• configloader.py: Cleanup expired certs and sync to strongSwan on startup

[cla-bot]

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[cla-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have the users @allen12921 on file. In order for us to review and merge your code, please contact the project maintainers via info@strongswan.org to get yourself added.