Enable OTLP retry by default in autoconfigure

[jack-berg]

While the RetryPolicy class and configuring RetryPolicy on OTLP exporters has been stable since 1.28.0, the autoconfigure retry option OTEL_EXPERIMENTAL_EXPORTER_OTLP_RETRY_ENABLED still defaults to false.

The OTLP exporter specification doesn't mince words on this:

Transient errors MUST be handled with a retry strategy.

Its quite clear that exporters need to retry.

But as opentelemetry-specification#3639 points out, there are some outstanding issues with the retry language in the specification. The argument against enabling retry by default in autoconfigure is that the spec could potentially change in ways incompatible with the java default behavior we land on, and we would be unable to change the configuration later.

So we're in a tough position: the spec clearly says that we should retry, but lacks details describing exactly how.

[jack-berg]

Oops, this is a duplicate of #5641. Closing. Please pick up any conversation on the other issue.