Extract log entries from events

[steve-hb]

Request

Alloy should be able to extract logs from otel span events using e.g. otelcol.connector.spanlogs.
Currently only the spanmetrics connector supports extracting events, but does not seem suitable for getting the logs into e.g. Loki.

Use case

Some libraries (e.g. uptrace otellogrus) have the (imo positive) tendency to put logs into span events improving the context of a structured log entry with the data available on the trace. Since other vendors (Elastic, Uptrace, Honeycomb) support this natively, I don't see the point not having this on Alloy.

Also the overhead of having more than one batch per application request (e.g. on Lambda when doing push ingestion for fast ingestion), would increase cost and complexity for many.
There is also a discussion about this on the otel collector: open-telemetry/opentelemetry-collector-contrib#3447