docs(Window): remove centered parameter

[Tsvetomir-Hr]

Related to: https://github.com/telerik/blazor/issues/8956

[dimodi]

• Explain how to center the Window initially by not using Top and Left at all, or y setting them to string.Empty.
• Enhance the "Top and Left" example with the button that centers the Window back.

[Tsvetomir-Hr]

• Explain how to center the Window initially by not using Top and Left at all*

For this, I can add at the beginning of the article that if these parameters are not defined the Window will be in the center. Is that good for you @dimodi ?

• Enhance the "Top and Left" example with the button that centers the Window back.*

If I update the example to center the window through a button what will be the purpose of the KB? #2821