Privacy fix for username-as-common-name

🔒 Privacy Fix for username-as-common-name

This fork fixes a privacy issue in the ignore-individuals feature when OpenVPN server uses the username-as-common-name option.

Problem

When the OpenVPN server is configured with username-as-common-name, the common_name field contains the actual username. The previous implementation would still export common_name as a label, leaking user information despite the privacy flag being enabled.

Solution

When ignore-individuals=true, all individual client data is now hidden by aggregating metrics:

• ✅ Counter metrics (bytes sent/received) are summed across all clients
• ✅ Gauge metrics (like route last reference time) use the most recent timestamp
• ✅ Only status_path label is exported
• ✅ common_name is NOT exported, preventing username leaks

Changes

• Add ignoreIndividuals flag to OpenVPNExporter struct
• Implement metric aggregation in collectServerStatusFromReader
• Remove common_name from labels when ignore-individuals=true
• Update README with clear documentation of aggregation behavior