Extend metrics in the code base

[otherview]

Description

Adds metrics to other parts of the code. Based on https://github.com/vechain/protocol-board-repo/issues/119

• Adds Gauge meter

• Adds following metrics:

• block_bft_committed_count [ finalized, proposed ]

• block_proposed_duration_ms [ failed, proposed ]

• block_proposed_count [ failed, proposed ]

• block_proposed_tx_count

• block_received_duration_ms [ failed, proposed ]

• block_received_count [ failed, proposed ]

• block_received_processed_tx_count

• chain_fork_count

• chain_fork_size

• p2p_connected_peers_count

• p2p_discovered_node_count

• p2p_dial_new_node_count

• txpool_current_tx_count [ remote, local ] [ total ]

Type of change

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

No changes to current running code.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] New and existing E2E tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have not added any vulnerable dependencies to my code

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 72.52747% with 75 lines in your changes are missing coverage. Please review.

Project coverage is 57.55%. Comparing base (e42227b) to head (6dd8cdf). Report is 17 commits behind head on pedro/add_metrics.

:exclamation: Current head 6dd8cdf differs from pull request most recent head 9735a3d. Consider uploading reports for the commit 9735a3d to get more accurate results

Files	Patch %	Lines
telemetry/prometheus.go	83.43%	18 Missing and 9 partials :warning:
cmd/thor/node/node.go	0.00%	18 Missing :warning:
cmd/thor/node/packer_loop.go	0.00%	18 Missing :warning:
api/events/events.go	0.00%	3 Missing :warning:
api/transfers/transfers.go	0.00%	3 Missing :warning:
p2psrv/nodes.go	0.00%	2 Missing :warning:
p2psrv/server.go	0.00%	2 Missing :warning:
telemetry/telemetry.go	86.66%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## pedro/add_metrics #684 +/- ## ===================================================== + Coverage 57.27% 57.55% +0.27% ===================================================== Files 156 159 +3 Lines 17218 17460 +242 ===================================================== + Hits 9862 10049 +187 - Misses 6392 6438 +46 - Partials 964 973 +9 ```

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