Enable mTLS for Nexus metrics

Since https://repo1.dso.mil/platform-one/big-bang/apps/core/monitoring/-/issues/71 is complete, Prometheus is configured with certs to properly scrape metrics from Istio injected applications.

This ticket should encompass:

• Configuring the servicemonitor/podmonitor for TLS scraping following this doc (sections for servicemonitor and podmonitor config)
• Removing the mTLS "exception" for the metrics port
• Validating all application functionality + metrics scraping