Add use-page-header-tools

[redallen]

use-page-header-tools (#4223)

• PageHeader: avatar prop was removed. Add the avatar to the PageHeaderTools component instead (which is passed into PageHeader via the headerTools prop.
• PageHeader: toolbar prop was removed. Use the headerTools prop instead. Also, if you previously used the Toolbar, ToolbarGroup, or ToolbarItem components for the header, replace them with the PageHeaderTools, PageHeaderToolsGroup, and PageHeaderToolsItem components.