metrics: add metrics monitoring system CPU and memory

[c98tristan]

Prerequisite: 

• Merge this PR first: metrics, core: add Prometheus metrics collector, add some metrics support #497

Information

This pull request introduces significant changes to the system monitoring metrics, including the addition of new metrics and the refactoring of existing ones.

CPU Metrics Implementation:

• Added new files to handle CPU metrics collection, including platform-specific implementations (metrics/cpu.go, metrics/cpu_disabled.go, metrics/cpu_enabled.go, metrics/cputime_nop.go, metrics/cputime_unix.go). [1] [2] [3] [4] [5]
• Update and add some memory monitoring metrics collection.

Reference:

• core, ethdb, metrics, p2p: expose various counter metrics for grafana ethereum/go-ethereum#19692
• metrics: gather and export threads and goroutines ethereum/go-ethereum#19725
• metrics: disable CPU stats (gosigar) on iOS ethereum/go-ethereum#20816