gtkdialog.info file is not installed by meson

[rbtylee]

The gtkdialog.info file is created by meson. I was using the docs option in the build. But it is not installed on the system by ninja -C build install. This is presumably the same situation using the automake build system, although I did not test it. This was on Bodhi Linux 7 (Ubuntu 22.04).

I also noted the gtkdialog.info file created lacks the info dir entry which caused a lintian warning when I packaged it for Bodhi Linux (Ubuntu 22.04 base). I altered the beginning of the generated file to:

This is gtkdialog.info, produced by makeinfo version 6.8 from
gtkdialog.texi.
INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* gtkdialog.info: (gtkdialog.info).      GUI creation tool for scripting
END-INFO-DIR-ENTRY
This manual documents version 0.8.5 of the Gtkdialog utility.

to satisfy lintian and make the info command properly work for the info dir.