[Docs] Clarify the retro-active property of Loki in the retention docs

Hi Loki maintainers,

In the latest version of the docs on storage and retention (https://grafana.com/docs/loki/latest/operations/storage/retention/#compactor), there is a statement saying

Changes to your retention period are not retroactive, that is, they are not applied to logs that have already been ingested.

Does that mean that all the logs that were ingested prior to my change of the retention period will never be deleted by the compactor?

I initially opened a forum topic to ask about this, but it does seem like it's slightly confusing. I wonder if this note could use an example.