[LYN-2522] Filtering for gem catalog (#867)

* Added sort filter proxy model for gem model that can filter based on name, gem origin, supported platform, features and/or types.
* Added new filter pane on the left with several filter categories for gem origin, type, platform and feature.
* Added filter category widget which is a collapsable generalized checkbox group that can interact with the proxy model and thus control filtering.
* Removed fixed size of the project manager. The application should always be resizable.

Code/Tools/ProjectManager/Source/ProjectManagerWindow.cpp

@@ -32,8 +32,6 @@ namespace O3DE::ProjectManager
         layout->setSpacing(0);
         layout->setContentsMargins(0, 0, 0, 0);
 
-        setFixedSize(this->geometry().width(), this->geometry().height());
-
         m_pythonBindings = AZStd::make_unique<PythonBindings>(engineRootPath);
 
         m_screensCtrl = new ScreensCtrl();