Enable mTLS for Neuvector metrics

• Ensure ServiceMonitor has the appropriate config to enable mTLS scraping of metrics.
• Relocate PeerAuthentication file to root of bigbang/ directory
• Remove BB override for mTLS (added in big-bang/bigbang!2558 (merged)), so that mTLS is STRICT by default

See reference: https://repo1.dso.mil/big-bang/product/packages/monitoring/-/blob/main/docs/istio-mtls-metrics.md#servicemonitor-config