Describe the bug

Currently, there are three separate sources for OSI documentation hosted online:

The main Antora documentation at: opensimulationinterface.github.io/osi-antora-generator
The OSI v3.5.0 Antora documentation at: opensimulationinterface.github.io/osi-documentation/
The Doxygen documentation at: https://opensimulationinterface.github.io/open-simulation-interface/

Describe how to reproduce the bug

Visit the links mentioned above.
Observe that the documentation is split across three sources.

Describe the expected behavior

A unified and streamlined documentation experience. Specifically, the following changes are recommended:

Remove the dedicated hosting for the OSI v3.5.0 documentation.
Redirect opensimulationinterface.github.io/osi-documentation to point to the latest version hosted at opensimulationinterface.github.io/osi-antora-generator.
Since the full content of the Doxygen documentation is already included in the Antora-generated documentation, there is no need for a separate Doxygen-hosted version. Therefore, the standalone Doxygen documentation should be removed.

Source issue

This is a copy of the description in issue OpenSimulationInterface/open-simulation-interface#832.
This was necessary to make linked changes for all relevant repositories with an issue in each of them.