Add Initial Gem Repository Management Screen (#4172)

* Adds the gem repo screen with the UI built but with mocked data and not connected to the o3de scripts

Signed-off-by: nggieber <nggieber@amazon.com>

* Changed name of added to enabled, disabled define, removed unused functions

Signed-off-by: nggieber <nggieber@amazon.com>

* Added eof nl to qss

Signed-off-by: nggieber <nggieber@amazon.com>

Code/Tools/ProjectManager/Source/ScreenDefs.h

@@ -23,7 +23,9 @@ namespace O3DE::ProjectManager
         Projects,
         UpdateProject,
         UpdateProjectSettings,
-        EngineSettings
+        Engine,
+        EngineSettings,
+        GemRepos
     };
 
     static QHash<QString, ProjectManagerScreen> s_ProjectManagerStringNames = {
@@ -34,7 +36,9 @@ namespace O3DE::ProjectManager
         { "Projects", ProjectManagerScreen::Projects},
         { "UpdateProject", ProjectManagerScreen::UpdateProject},
         { "UpdateProjectSettings", ProjectManagerScreen::UpdateProjectSettings},
-        { "EngineSettings", ProjectManagerScreen::EngineSettings}
+        { "Engine", ProjectManagerScreen::Engine},
+        { "EngineSettings", ProjectManagerScreen::EngineSettings},
+        { "GemRepos", ProjectManagerScreen::GemRepos}
     };
 
     // need to define qHash for ProjectManagerScreen when using scoped enums