Add support for controlling LLM visibility

[augustuswm]

We want to provide a way to safely provide (non-public) RFD content to LLMS. As opposed to the public vs private flag, this instead should be considered a property of the revision itself and therefore can be embedded in documents as an attribute. This will be an open by default control that allows RFDs to opt out of the LLM safe dataset.

Users of the API and CLI should be able to request all RFD data or specifically only LLM safe data from any endpoint that reads RFD data.

The primary goal here is to make the LLM safe dataset as easy to use as possible.