Move otbExternalModuleTemplate repository from GitHub to gitlab.orfeo-toolbox.org

The source code of the official OTB remote module template is only available on GitHub at:

https://github.com/orfeotoolbox/otbExternalModuleTemplate

It would be better to move/fork it to a new projects gitlab.orfeo-toolbox.org and mirror it on GitHUb like other otb git repositories

Edited by Manuel Grizonnet