/usr/share/vim/addons/ftdetect/icinga2.vim is in vim-icinga2 2.8.1-0ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | " Modify
au BufNewFile,BufRead /*etc/icinga2/*.conf,/*usr/share/icinga2/include/{itl,plugins,*.conf} set filetype=icinga2
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