improve tidb go runtime metrics

## Enhancement

- Background
Currently, TiDB's monitoring related to the Golang runtime lacks sufficient detail to effectively identify runtime-related issues. To address this, we need to enhance the existing Grafana monitoring panels and introduce additional monitoring metrics focused on the Golang runtime.
- Objectives
The primary goal is to refine and expand the TiDB monitoring capabilities to provide more insightful data, which will aid in diagnosing runtime-related problems. The improvements will be implemented by optimizing the existing monitoring panels and adding new ones to cover critical runtime aspects.
- Tasks
- [x] Enhance the readability and clarity of the tidb-runtime -> memory usage monitoring panel. https://github.com/pingcap/tidb/pull/55391
- [x] Introduce a new panel to monitor CPU time of runtime jobs. https://github.com/pingcap/tidb/pull/55401
- [x] Refine the GC STW monitoring panel to provide more actionable insights. https://github.com/pingcap/tidb/pull/55982
- [x] Implement new panels to monitor ~scheduler activity and~ mutex contention, offering better visibility into potential bottlenecks. https://github.com/pingcap/tidb/pull/56022
- [x] Introduce new panels for golang gc rate and GOGC/GOMEMLIMIT. https://github.com/pingcap/tidb/pull/56033 https://github.com/pingcap/tidb/pull/56039
- [x] Introduce new panels for heap alloc and heap free. https://github.com/pingcap/tidb/pull/56050

The issue names no files, tests, or entry points; review the linked pull requests to understand the monitoring-panel and Go runtime metric changes. The checklist shows every task as complete, so there is no remaining scope identified for a new contributor.

Written by the indexing model from the issue text.