Issue 51031 UI - transition between two instances needs improvement
    
    Bug Description:  When you switch between instances in the UI, there is
                      no loading page, there is a long wait before the dropdown
                      menu changes, and it does not refresh the page content
                      (it still contains the previous instance's data).
    
    Fix Description:  Set the "loading" flag and the serverId right away when
                      instance is changed.   Then we set the tab component's
                      key to the server ID so the content is automatically
                      refreshed.
    
    fixes: https://pagure.io/389-ds-base/issue/51031
    
    Reviewed by: spichugi(Thanks!)