feat: Support OTEL metrics

[chtushar]

Description

Add a OTel metrics support so that the OpenAPM emits metrics in OTLP format and directly pushes it to a OTLP compatible endpoint like vmagent or Otel collector.

OpenAPM should have a mode option and should have two modes namely openmetrics (default) and opentelemetry.

const openapm = new OpenAPM({
    mode: 'opentelemetry'
})