Improve telemetry wrapper clarity

(quoting @alco, followup from https://github.com/electric-sql/electric/pull/3110)

We are currently wrapping :telemetry.execute() calls inside Electric.Telemetry.OpenTelemetry which obscures the fact that those metrics are used not only by our OpenTelemetry exporter but also the Prometheus and CallHomeReporter ones. At the same time the name get_stack_span_attrs() doesn't reflect the fact that those attrs are also put on metrics, not only spans.

We should refactor some of the telemetry to reflect this fact.