patch 9.1.0110: filetype: add 'Config.in' filetype detection

patch 9.1.0110: filetype: add 'Config.in' filetype detection

The 'Config.in' file type is for Buildroot configuration files.
Buildroot Config.in files use the same Kconfig backend as the Linux
kernel's Kconfig files.

Buildroot also has other filename variants that follow "Config.in.*",
they are used to distinguish multiple Config.in files in the same
directory.

See https://buildroot.org/downloads/manual/manual.html#_literal_config_in_literal_file

closes: #14038

Signed-off-by: Brandon Maier <brandon.maier@collins.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>