Add feature/hint to trim irrelevant fields from sample events

In the past we had been curating the sample events so as to remove any additional field like `host` which adds more noise to the docs instead of improving the sample event. After not making it a rule we starting being more flexible on this but today it is an open question if we should or not perform curations horizontally and even more make it an official proposal. I don't think we can automate the removal of those since in some cases these might be actually needed.

Start by reviewing how elastic-package generates or curates sample events and where extra fields such as `host` are handled. The issue does not name files, tests, or an entry point; done would require an agreed proposal for whether and how irrelevant fields should be trimmed, with clear behavior for fields that are needed.

Written by the indexing model from the issue text.