FR: Override hidden ancestors log node template

[eproxus]

Is your feature request related to a problem? Please describe. When trying to style the log nodes with custom characters, the log node of hidden ancestors is not overridable.

Describe the solution you'd like It would be nice if the log_node template would be used for these nodes too.

Describe alternatives you've considered None.

Additional context See example and discussion here: https://github.com/jj-vcs/jj/discussions/6643

[yuja]

The bottom ~ in the example of https://github.com/jj-vcs/jj/discussions/6643 doesn't represent a node, but is an edge drawing. We'll need something like https://github.com/jj-vcs/jj/issues/4904 to customize it.