feat(sequencer): Declare Metrics trait and implement it for prometheus

[RomanHodulak]

Ticket

• Related Linear Ticket: SEQ-199

What does this PR do?

• Summary: Introduces the concept of application "metrics." for collecting data about the application usage. The main implementation technology is prometheus.
• Key Changes:
  • Add Metrics trait.
  • Make send raw tx endpoint dependent on Metrics
  • Record every call on the endpoint
  • Add endpoint for prometheus scraper

Does this PR introduce any breaking changes (API/schema)?

• *No

Do any environment variables need to be updated or added before deployment?

• No

How can this PR be tested?

Every call to eth_sendRawTransaction is counted and added to the output of metrics endpoint.

[linear]

SEQ-199 Prometheus metrics + instrumentation

Ahead of the private testnet, we need to have endpoints and any other relevant paths instrumented and emitting basic metrics usable by node operators.

AC:

• Support an open source observability stack, like Prometheus
• Main flows (e.g. send_raw_transaction() instrumented)

[daniilrrr]

lgtm