Add metrics in txpool

[trinhdn2]

Prerequisite

• Refactor metrics package with Prometheus and InfluxDB support #428

Checklist

• Add more and convert current txpool metrics from counter to meter.
• Remove priced txs in batch for some cases and add a timer metric for priced tx list reheap operation.

Added metrics:

• txpool_pending_discard
• txpool_pending_replace
• txpool_pending_ratelimit
• txpool_pending_nofunds
• txpool_queued_discard
• txpool_queued_replace
• txpool_queued_ratelimit
• txpool_queued_nofunds
• txpool_queued_eviction
• txpool_known
• txpool_valid
• txpool_invalid
• txpool_underpriced
• txpool_pending
• txpool_queued
• txpool_local
• txpool_reheap
• txpool_reheap_count

Example of new metrics under prometheus format:

# TYPE txpool_invalid gauge
txpool_invalid 119247

# TYPE txpool_known gauge
txpool_known 3337375

# TYPE txpool_local gauge
txpool_local 0

# TYPE txpool_pending gauge
txpool_pending 265

# TYPE txpool_pending_discard gauge
txpool_pending_discard 171

# TYPE txpool_pending_nofunds gauge
txpool_pending_nofunds 1

# TYPE txpool_pending_ratelimit gauge
txpool_pending_ratelimit 0

# TYPE txpool_pending_replace gauge
txpool_pending_replace 33

# TYPE txpool_queued gauge
txpool_queued 0

# TYPE txpool_queued_discard gauge
txpool_queued_discard 0

# TYPE txpool_queued_eviction gauge
txpool_queued_eviction 0

# TYPE txpool_queued_nofunds gauge
txpool_queued_nofunds 0

# TYPE txpool_queued_ratelimit gauge
txpool_queued_ratelimit 0

# TYPE txpool_queued_replace gauge
txpool_queued_replace 0

# TYPE txpool_reheap_count counter
txpool_reheap_count 18416

# TYPE txpool_reheap summary
txpool_reheap {quantile="0.5"} 70105
txpool_reheap {quantile="0.75"} 84645
txpool_reheap {quantile="0.95"} 109613
txpool_reheap {quantile="0.99"} 145931.7
txpool_reheap {quantile="0.999"} 194394.28000000003
txpool_reheap {quantile="0.9999"} 194559

# TYPE txpool_underpriced gauge
txpool_underpriced 0

# TYPE txpool_valid gauge
txpool_valid 46236

References:

• core, ethdb, metrics, p2p: expose various counter metrics for grafana ethereum/go-ethereum#19692
• core: fix queued transaction eviction ethereum/go-ethereum#21300