Add option to remove close button in dialog header

[sezaru]

Currently we can disable modal to close via close_on_click_away and close_on_escape, but we still don't have an option to hide/remove the X button on the modal top right.

We need an option to that in scenarios where we want full control when the modal is closed.

[nhobes]

Done in https://github.com/petalframework/petal_components/releases/tag/v1.5.5