Allow TitleBar Header customization

[Paliverse]

Is your feature request related to a problem? Please describe

No.

Describe the solution you'd like

I would like to be able to manipulate the TitleBar's Header content to be able to set UI elements how i see fit. Horizontal alignment to be Left, center, or right etc..

Describe alternatives you've considered

N/A

Additional context

N/A

[botder]

I was using the Header content to display a Menu on the left side of the title bar in the previous version. Now it's impossible to push the menu all the way to the left and it's always stuck to the right side of the title bar.

It would be great if the template used {TemplateBinding HorizontalContentAlignment} here: https://github.com/lepoco/wpfui/blob/303f0aefcd59a142bc681415dc4360a34a15f33d/src/Wpf.Ui/Controls/TitleBar/TitleBar.xaml#L151

[chucker]

See #775, #1025, #1030