Move ObservedEvent into crates/telemetry, consolidated with self_tracing::LogRecord

[jmacd]

The ObservedEvent has associated flume channels and a connection with the existing metrics and admin component which make it an appealing way to transport log events in the engine.

Move PipelineKey, DeployedPipelineKey, CoreId types into crates/config.

Therefore, moving ObservedEvent into crates/telemetry lets us (optionally) use the same channel already use for lifecycle events for tokio log records. The existing event structure is extended with a EventMessage enum which supports None, String, or LogRecord messages. This way we can use a log record as the event message for all existing event types. The event.rs file moves, only ObservedEventRingBuffer from that file remains in crates/state.

The LogRecord has been storing a timestamp. Now, we leave that to the ObservedEvent struct. LogRecord passes through SystemTime everywhere it has been used. Callers generally compute this and pass it in. Minor cleanup in self_tracing/formatter.rs, do not pass SavedCallsite it can be calculated from record metadata as needed.

In internal_events, the raw_error! macro has been replaced with a helper to generate LogRecord values first, by level. This lets us pass info_event!("string", key=value) to any of the event constructors and construct an OTLP bytes message instead of a String message.

[codecov]

Codecov Report

❌ Patch coverage is 52.65700% with 98 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.40%. Comparing base (8470d2d) to head (1abe9fd).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1818      +/-   ##
==========================================
- Coverage   84.40%   84.40%   -0.01%     
==========================================
  Files         497      498       +1     
  Lines      145422   145469      +47     
==========================================
+ Hits       122740   122778      +38     
- Misses      22148    22157       +9     
  Partials      534      534              

Components	Coverage Δ
otap-dataflow	85.68% <52.65%> (-0.01%)	⬇️
query_abstraction	80.61% <ø> (ø)
query_engine	90.52% <ø> (ø)
syslog_cef_receivers	∅ <ø> (∅)
otel-arrow-go	53.50% <ø> (ø)
quiver	90.66% <ø> (ø)

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