Add metrics OTLP exporter

[codeboten]

Bring back the OTLP exporter using the new metrics SDK

• Add support for Sum
• OTLP Exporter: Add support for Gauge point types #2385
• OTLP Exporter: Add support for Histogram point types #2386

[codeboten]

Closing this issue as the exponential histogram issue can be addressed separately and isn't a blocker for GA