Please describe the feature request.
OTLP format supports delta and cumulative temporality. Currently the OTLP registry does not make this configurable and cumulative is always sent. While this should work for compliant OTLP receivers, as far as I understand, some users may have a preference for one and we could support making this configurable.

Rationale
OTLP explicitly does not have a preference of aggregation temporality. Since OTLP is not tied to a specific metrics backend, there is less reason for us to use one temporality over the other.

Additional context
See initial discussion: #3129 (comment). There is prior art in that the SimpleMeterRegistry allows configuring whether it is cumulative or step based.
/cc @twicksell