Have a "stage specific lines" flow with `log_pager`

[nihaals]

Is your feature request related to a problem? Please describe.

Setting a log_pager helps make diffs more readable, but if it does anything other than simple changes such as colors, selecting a range of lines to do e.g. a partial stage breaks. If you select a line, it will actually stage a lower line due to Neogit not being aware of how the lines have been rearranged in the view. This means you have to choose between a workflow allowing you to select specific lines and using a thorough log_pager.

Describe the solution you'd like

It would be great if there was a way to customise when log_pager is used. This would likely have to be a toggle as there is value in both selecting specific lines and seeing a pretty diff on the main NeogitStatus page. Being able to quickly toggle between the selectable view and the log_pager view would mean you could go from understanding the diff to actually staging it efficiently.

Describe alternatives you've considered

You can choose between using log_pager and selecting specific lines but ideally you could do both.