[monitoring] Add metrics for external-scheduler

[NikolayDemchuk]

Description

Add grafana dashboard for go-related metrics and re-label metrics for scheduler-extender

Why do we need it, and what problem does it solve?

Adds observability on internal go binaries' runtimes

What is the expected result?

Scheduler-extender is eligible for observation and load tests

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.