KiCadDocumentation.cmake: fix install target for HTML docu

KiCadDocumentation.cmake: fix install target for HTML docu

The old default behaviour while installing the generated HTML content is
to install the whole images/$LANG folders into every generated language.
This was producing a lot of useless duplicated data.  After applying a
commit from upstream [1] this problem was partially fixed, but the
default images were not installed.

This commit fixes changing the kind of creating the list for the default
images that will be installed in a next step. Also the images from the
English language is needed as some howtos use them.

[1] https://github.com/KiCad/kicad-doc/commit/027c096941105048da8921ac2d8bc4d1594b14a9

Gbp-Pq: Topic fixes
Gbp-Pq: Name KiCadDocumentation.cmake-fix-install-target-for-HTML-docu.patch