[REQUEST]: Prepare public documentation for the distribution helper tool for Package Registry

### Description

We are introducing a new tool to help creating Package Registry distributions.

This helps solving a usual concern with the big size of our published distribution images. This new tool helps maintaining custom images with the packages each user needs.

### Resources

This tool is being introduced on these PRs, that include reference docs:
* https://github.com/elastic/package-registry/pull/1335
* https://github.com/elastic/package-registry/pull/1554

### Collaboration

TBD. The docs and product team will work together to determine the best path forward.

### Point of contact.

**Main contact:** @jsoriano

**Stakeholders:** @nimarezainia

cc @theletterf @fred-maussion @kpollich