Add module to provide API for export metrics to OpenTelemetry

I created the opentelemetry_metrics submodule which provides Metrics API - here is the MR https://git.drupalcode.org/project/opentelemetry/-/merge_requests/49

Please review and test it on your side before merging.

Created a submodule "opentelemetry_metrics" with the OpenTelemetry Metrics API as a Drupal service opentelemetry.metrics.