Fix automatic loading for some gui plugins

Gui plugins created with new CMake style get the added suffix '_qt_plugin'. This allows to recognize plugins that do not end with the old 'GuiPlugin' suffix

requested review from @kartmann

assigned to @uhxkb_naumann

Thanks for preparing the MR @uhxkb_naumann

@dreher @reister:

Qt Plugins in modern ArmarX projects are not loaded automatically because the ArmarX Gui checks lib files for the ending "GuiPlugin.so"

There are two possible fixes:

1. Always append "_qt_plugin" to Qt plugin target names and check also for that (implemented in this MR)
2. Put (links to) Qt plugin so files into another directory than "lib" and have the gui search that one, assuming that all of them are Qt plugins.

Note: The Gui can handle so files which are not Qt plugins, but loading and checking many files this way is very slow, so we kind of need file-system-based mechanism to find the correct files.

We can also merge this MR first and implement option 2. later

approved this merge request

added 8 commits

• 94291ec9...9e67d43b - 7 commits from branch master
• 9d95ee76 - Merge branch 'master' into fix/gui-plugin-loading

Compare with previous version

enabled an automatic merge when the pipeline for 9d95ee76 succeeds

merged

mentioned in commit b8ff136c