Ideal pipeline for documented packages with many packages

[Datseris]

Hi,
I discussed on Slack what I would like to have as an ideal pipeline for documenting packages like DynamicalSystems.jl. Here it is:

• each package has standard Documenter.jl docs, or any docs that allow documenter syntax (@docs and @example blocks). For example: https://juliadynamics.github.io/Entropies.jl/dev/ . Each package builds and deploys its own docs as normal. Some cross-referenced links that point to docs of functions in different packages will not work, but that is okay. Having each package build its own docs is useful during development, because ideally each Pull Request should add its documentation, and we would like to be able to preview it.
• Hence, like Documenter.jl does, the documenting package I use should allow for documentation previews in pull requests.
• The central repo, for me DynamicalSystems.jl, includes all these docs. It could be done in the way it is done now, and puts a new side bar top-level entry for each package, https://juliadynamics.github.io/DynamicalSystems.jl/dev/ (in the Sidebar there is an expandable Entropies, or ChaosTools, or whatever entry)
• Alternative to the side bar is the overarching bar that SciML MultiDocumenter has, see the top of this page: https://docs.sciml.ai/Overview/stable/ . Either format is fine for me, I don't really care. I am using the side bar format now, but could give a try on the "top bar" format.
• In the DynamicalSystems.jl repo, I set up a github action that triggers its doc build every couple of days or so, so that if a package has a new release, the "central" docs are updated.
• The most important features I care about are: (1) cross-referencing documentation strings of other functions. E.g., Entropies has function foo that referneces function ChaosTools.bar and that reference is actually clickable in the built docs. (2) Being able to go to the source code of each function from the central documentation. At the moment, Documenter.jl allows accessing the source code of the function ONLY For the module that builds the docs.