feat: (metrics) integrate OTeL in duties and eth packages

[oleg-ssvlabs]

Background
The observability team is currently working on a metrics refactor to address various challenges with the current implementation. As part of this refactor, Prometheus SDKs are being replaced with OTeL SDKs, which are industry-leading in observability and provide an abstraction layer for various observability "backends". Additionally, OTeL SDKs will be used to implement Traces. This aspect should be taken into consideration.

Implementation

1. Central observability configurator was added (new root pkg observability). It looks simple, although it wasn't simple to decide what should "configurator" include mainly because OTeL supports two way of provider configuration - SDKs and environment variables and we want SSV Node users to be able to configure observability via native OTeL env vars. Some research showed that the vision of OTeL is "SDK first" meaning there are many features that aren't possible to configure via environment variables, yet possible via SDKs.However, the long-term aim is not to wrap OTeL environment variables into custom environment variables. Just FYI.

2. Multiple components were instrumented, including the Execution Client, Event Syncer, and Duty Scheduler. The following metrics were introduced (either new or replacements for old ones) along with their attributes:

• ssv.el.latency.duration (ssv.el.addr attributre)

• ssv.el.syncing.distance (ssv.el.addr attributre)

• ssv.el.syncing.status (ssv.el.addr, ssv.el.status attributre)

• ssv.el.syncing.last_processed_block (ssv.el.addr attributre)

• ssv.event_syncer.handler.events_processed (ssv.event_syncer.event_name attributre)

• ssv.event_syncer.handler.events_failed (ssv.event_syncer.event_name attribute attributre)

• ssv.event_syncer.handler.last_processed_block

• ssv.operator.duty_scheduler.slot_ticker_delay.duration

• ssv.operator.duty_scheduler.executions (ssv.duty.type attributre)

• ssv.operator.duty_scheduler.committee_executions (ssv.runner.role attributre)

3. Conventions.md which describes OTeL metric related conventions (mainly naming). Will continuously be updated. Conventions (are described in the document) are based on OTeL original conventions. Although, in some cases OTeL's ambiguity was tightened.