docs: add Grafana Metrics vulnerability report (fixes #124)

[Proxypentest]

Summary

This PR adds a detailed security report regarding the publicly exposed Grafana /metrics endpoint, which leads to internal server information disclosure.

References

Fixes: #124

### Impact

Possible Exploitation Outcomes:
Unauthorized profiling of backend infrastructure

Visibility into server load and performance trends

Ability to plan resource exhaustion (DoS) attacks with precision

Identification of potential weak points for further exploitation

Note: Public exposure of operational data like this violates security best practices and the principle of least privilege — such endpoints should not be exposed to unauthenticated users.

[jackieaxb]

@all-contributors please add @Proxypentest for security

Please note that this action does not indicate your pull request has completed the review process. Our security team still needs to validate your submission. The final announcement—regarding whether your submission qualifies for a bug bounty—will be made within the timeframe specified in our Bountybug readme file

[allcontributors]

@jackieaxb

I've put up a pull request to add @Proxypentest! 🎉