AirGapped environment don't have available all packages from epr.elastic.co

Hi, I have few airgapped clusters running on my employer.

I tried to use `docker.elastic.co/package-registry/distribution:9.x.x` and `docker.elastic.co/package-registry/distribution:production` and appears some packages or not been added to the container images, one of them is `system_otel`, which right now is necessary for my PoC, since we are moving to use OpenTelemetry entirelly, and use OTel Collector as Agent and EDOT Collector as Gateway.

I tried to proxy `epr.elastic.co` on Nexus but I am getting a few issues, which can be related to Nexus, or not.
For more information about this I have posted on [Discourse/Discuss](https://discuss.elastic.co/t/opentelemetry-integration-on-airgapped-environment/).

The `system_otel` can be found in [here](https://epr.elastic.co/package/system_otel/0.2.5/), and it state is in beta, but the documentation say about the epr been production ready.

> production: docker.elastic.co/package-registry/distribution:production - Packages available in the production registry (https://epr.elastic.co/). This image is updated every time a new version of a package gets published.

Start with the production distribution image and the epr.elastic.co system_otel/0.2.5 entry point, then compare the packages included in the image with those exposed by the registry. Investigate whether the missing package is a publishing or image-build issue, or whether Nexus proxying is responsible. Done means the air-gapped image exposes the required package or the limitation and supported procedure are documented.

Written by the indexing model from the issue text.