enh(test): install UI unit test headers to allow testing of apps in client apps

Description

We do not install the headers of the ui_test library, thus we can not write any UI test in our client repositories. This merge-request fixes this by excluding only unit-tests folders and not everything that starts with "test*".

How to test it?

This can really be tested with another repository.

However, it can be also verified manually that we only included the wanted files and not another by doing a file tree comparison between two versions of the sight archive. You can use meld for that.

Actually I did it and here is the only new files, which is what is expected: