feat: add prometheus monitoring

[rafaelcr]

Also creates and starts a prometheus server when service start is used.

Metrics included (example):

# HELP last_indexed_block_height The latest Bitcoin block indexed for ordinals.
# TYPE last_indexed_block_height gauge
last_indexed_block_height 859867
# HELP last_indexed_inscription_number The latest indexed inscription number.
# TYPE last_indexed_inscription_number gauge
last_indexed_inscription_number 75484947
# HELP registered_predicates The current number of predicates registered to receive ordinal events.
# TYPE registered_predicates gauge
registered_predicates 1

Adds new config:

[network]
prometheus_monitoring_port = 9153

Fixes #282

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 24.21053% with 72 lines in your changes missing coverage. Please review.	Files with missing lines	Patch %	Lines
components/ordhook-core/src/utils/monitoring.rs	36.36%	35 Missing :warning:
components/ordhook-core/src/service/mod.rs	0.00%	22 Missing :warning:
...c/core/pipeline/processors/inscription_indexing.rs	0.00%	5 Missing :warning:
components/ordhook-cli/src/cli/mod.rs	0.00%	4 Missing :warning:
components/ordhook-core/src/db/mod.rs	0.00%	4 Missing :warning:
components/ordhook-cli/src/config/file.rs	0.00%	1 Missing :warning:
components/ordhook-core/src/service/observers.rs	0.00%	1 Missing :warning:

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