tracing-opentelemetry 0.17.4

This release adds optional support for recording std::error::Errors using
[OpenTelemetry's semantic conventions for exceptions][exn-semconv].

Added

• Layer::with_exception_fields to enable emitting exception.message and
  exception.backtrace semantic-convention fields when an Error is recorded
  as a span or event field (#2135)
• Layer::with_exception_field_propagation to enable setting exception.message and
  exception.backtrace semantic-convention fields on the current span when an
  event with an Error field is recorded (#2135)

Thanks to @lilymara-onesignal for contributing to this release!