Mark as deprecated the qgis otb plugin

The qgis otb plugin can be deprecated I think. How do that ?

Archive the project on the gitlab ? Add a mention in the readme ?

For information the list of official packages provided by QGIS : QGIS Installers

Clean all mention of this plugin in the documentation.

Since QGIS 3.8, this plugin is part of QGIS’s source code. It is not required anymore. People using older versions of QGIS still need this plugin. But those old versions of QGIS are deprecated (QGIS 3.6 went out 2 years ago), so it makes sens to deprecate this plugin too.
I vote in favor of the deprecation.