Add support for emitting exceptions as logs

[trask]

Span events are in the process of being deprecated.

There are still some details to work on in semantic conventions, but I'm hoping that we can bundle this breaking change into 3.0.

TODO

• Introduce OTEL_SEMCONV_EXCEPTION_SIGNAL_OPT_IN semantic-conventions#3363
• [DRAFT] Start to add opt-in support for emitting exceptions as logs #16049