Add OTLP/HTTP metric exporter

[codeboten]

As with the other signals, metrics should be available for export as OTLP over HTTP.

[RangelReale]

For a use of this instead of gRPC, when running in a Lambda, the service is paused while not running. As gRPC keeps a persistent connection, this pause can make the connection be broken, and a reconnection would be needed when unpausing.

With an HTTP connection, only when flushing the connection is made, so this problem doesn't happen.